TL;DR: try recompiling everything. You can ask emacs to, or you can just force it to:
```bash
find ~/.emacs.d -name "*.elc" -delete
```
Then restart emacs.
----
The main culprits for this error are:
* some symbol is being interpretted as a function when it shoudln't be (i.e. [there is a syntax error](https://github.com/sinewalker/dotspacemacs/commit/979d01a#diff-6e8a7b5022a8063462bf49524307980eL191))
* some function is being called that does not exist, or has not been loaded by emacs
In the first case, *check your own init files for syntax errors*. Somtimes starting emacs with `--debug-init` helps, at least to narrow down which layer or init file might contain the mistake. Then you can search through your recent commits on those. When you search, try looking for the symbol beginning with an open paren:
`(some-package-fuction`
----
Very often what usually happens is that an emacs package is updated and the names of functions have changed. Breaking [Rule A](http://milosophical.me/pg/4-bit-rules.html). This happens depressingly often, especially with Org Mode.
Anyway, though the calling packages might be updated, you usually won't get benefit of that until you force emacs to re-compile all your elisp. To do that, remove the byte-compiled files. This gets rid of them all:
```bash
find ~/.emacs.d -name "*.elc" -delete
```