Specifically, it says:

Error while decoding: (invalid-state Bogus value for `default-process-coding-system' nil)

Now, I can't say I know what I'm doing (or that this works on GNU
Emacs), but this fixed it for me:

2006-05-20  Michael Sperber  <sperber@deinprogramm.de>

	* uudecode.el (uudecode-decode-region-external): Use '(binary
	. binary) for `default-process-coding-system' instead of nil to
	keep `call-process-region' from barfing.