You should be able to reproduce by pulling the develop branch, updating emacs packages and trying to jack-in with any project.

I am unable to replicate the issue with cider-jack-in-clj command. The full command used by CIDER is

[nREPL] Starting server via /usr/local/bin/clojure -Sdeps '{:deps {nrepl/nrepl {:mvn/version "1.0.0"} cider/cider-nrepl {:mvn/version "0.30.0"}} :aliases {:cider/nrepl {:main-opts ["-m" "nrepl.cmdline" "--middleware" "[cider.nrepl/cider-middleware]"]}}}' -M:cider/nrepl

My initial thoughts are something else is being included when using cider jack-in, check for a .dir-locals.el file. Or Emacs was not restarted after the packages were installed. Or it could be a faulty package download. Try move the cider packages out of the spacemacs elpa directory and restart Emacs to download packages again

I deleted my cider packages an restarted, but that didn't help. So strange. I had this working yesterday before updating. Here is my error mostly in full:

Starting new CIDER session ...
[nREPL] Starting server via "c:/Users/Paul Dumais/scoop/shims/clojure.exe" -Sdeps '{:deps {nrepl/nrepl {:mvn/version "1.0.0"} cider/cider-nrepl {:mvn/version "0.30.0"}} :aliases {:cider/nrepl {:main-opts ["-m" "nrepl.cmdline" "--middleware" "[cider.nrepl/cider-middleware]"]}}}' -M:cider/nrepl
error in process sentinel: nrepl-server-sentinel: Could not start nREPL server: Error building classpath. Don't know how to create ISeq from: clojure.lang.Symbol

java.lang.IllegalArgumentException: Don't know how to create ISeq from: clojure.lang.Symbol

	at clojure.lang.RT.seqFrom(RT.java:557)

	at clojure.lang.RT.seq(RT.java:537)

	at clojure.core$seq__5467.invokeStatic(core.clj:139)

	at clojure.core$merge_with$merge2__6033.invoke(core.clj:3083)

	at clojure.lang.ArrayChunk.reduce(ArrayChunk.java:63)

	at clojure.core$reduce1.invokeStatic(core.clj:944)

	at clojure.core$reduce1.invokeStatic(core.clj:936)

	at clojure.core$merge_with.invokeStatic(core.clj:3076)

	at clojure.core$merge_with.doInvoke(core.clj:3068)

	at clojure.lang.RestFn.applyTo(RestFn.java:139)

	at clojure.core$apply.invokeStatic(core.clj:669)

	at clojure.tools.deps$merge_edns.invokeStatic(deps.clj:141)

	at clojure.tools.deps.script.make_classpath2$run_core.invokeStatic(make_classpath2.clj:86)

	at clojure.tools.deps.script.make_classpath2$run.invokeStatic(make_classpath2.clj:153)

	at clojure.tools.deps.script.make_classpath2$_main.invokeStatic(make_classpath2.clj:203)

	at clojure.tools.deps.script.make_classpath2$_main.doInvoke(make_classpath2.clj:174)

	at clojure.lang.RestFn.applyTo(RestFn.java:137)

	at clojure.lang.Var.applyTo(Var.java:705)

	at clojure.core$apply.invokeStatic(core.clj:667)

	at clojure.main$main_opt.invokeStatic(main.clj:514)

	at clojure.main$main_opt.invoke(main.clj:510)

	at clojure.main$main.invokeStatic(main.clj:664)

	at clojure.main$main.doInvoke(main.clj:616)

	at clojure.lang.RestFn.applyTo(RestFn.java:137)

	at clojure.lang.Var.applyTo(Var.java:705)

	at clojure.main.main(main.java:40)

 ("exited abnormally with code 1")
error in process sentinel: Could not start nREPL server: Error building classpath. Don't know how to create ISeq from: clojure.lang.Symbol

java.lang.IllegalArgumentException: Don't know how to create ISeq from: clojure.lang.Symbol

	at clojure.lang.RT.seqFrom(RT.java:557)

	at clojure.lang.RT.seq(RT.java:537)

	at clojure.core$seq__5467.invokeStatic(core.clj:139)

	at clojure.core$merge_with$merge2__6033.invoke(core.clj:3083)

	at clojure.lang.ArrayChunk.reduce(ArrayChunk.java:63)

	at clojure.core$reduce1.invokeStatic(core.clj:944)

	at clojure.core$reduce1.invokeStatic(core.clj:936)

	at clojure.core$merge_with.invokeStatic(core.clj:3076)

	at clojure.core$merge_with.doInvoke(core.clj:3068)

	at clojure.lang.RestFn.applyTo(RestFn.java:139)

	at clojure.core$apply.invokeStatic(core.clj:669)

	at clojure.tools.deps$merge_edns.invokeStatic(deps.clj:141)

	at clojure.tools.deps.script.make_classpath2$run_core.invokeStatic(make_classpath2.clj:86)

	at clojure.tools.deps.script.make_classpath2$run.invokeStatic(make_classpath2.clj:153)

	at clojure.tools.deps.script.make_classpath2$_main.invokeStatic(make_classpath2.clj:203)

	at clojure.tools.deps.script.make_classpath2$_main.doInvoke(make_classpath2.clj:174)

	at clojure.lang.RestFn.applyTo(RestFn.java:137)

	at clojure.lang.Var.applyTo(Var.java:705)

	at clojure.core$apply.invokeStatic(core.clj:667)

	at clojure.main$main_opt.invokeStatic(main.clj:514)

	at clojure.main$main_opt.invoke(main.clj:510)

	at clojure.main$main.invokeStatic(main.clj:664)

	at clojure.main$main.doInvoke(main.clj:616)

	at clojure.lang.RestFn.applyTo(RestFn.java:137)

	at clojure.lang.Var.applyTo(Var.java:705)

	at clojure.main.main(main.java:40)

 ("exited abnormally with code 1")
Beginning of buffer [3 times]
Mark set
<left-fringe> <mouse-1> is undefined
Mark set 

I suggest trying an Emacs package rollback, there is a link to this on the Spacemacs home buffer (`SPC b h`)

If previously used packages no longer work, then perhaps something is wrong with the Java and/or Clojure tool installed on windows If packages do work, then it suggests there is an issue with one or more of the packages. Check which package has been updated recently (i.e. cider-nrepl was updated a few days ago)

I tried rolling back the packages I installed. Now I will try checking out a previous commit of spacemacs develop.

I went back pretty far and I still see the same error. I might have something to do with the state of my .m2 directory.

I tried deleting that, but the error occurs before attempting to download deps it seems.

I'm going to try a different test project.

I would be surprised if the Spacemacs code is related, there have only been a couple of commits to the clojure layer in the last year. Did something change with the scoop install of Java or Clojure ? The error message seems to suggest there is a bug in nrepl or something that is sent to nrepl, or possibly something in the code. If there is a user.clj file on the path, that can cause problems, but the error message would usually mention that namespace rather than nrepl. If there is a user.clj file and it has nrepl requires or related code, it could be causing an issue (assuming it exists or is on the path). I test issues such as this across multiple projects and create a new very simple Clojure project to test if needed

yeah, it seems not to be spacemacs relatead. I'll crosspost in a little bit when I have more info. Thanks!

I'm using a test project created by seancorfield's clj-new

Posted over on clj-on-windows.