I think I found a bug, how do I report it?
Usually you will get some help on the xcms mailing list. Good bug reports will save both you and the fellow users (or developers) time.
The long answer can be found in the Posting Guide of the bioconductor project, and most points also apply to xcms. Simon Tatham's essay on "How to Report Bugs Effectively" is not restricted to a particular programming language, but a very recommended read in general.
The short answer is:
Check the growing xcms FAQ
Report the shortest possible steps to reproduce the problem, even better try to reproduce it with the public faahKO data as e.g. in the PcaMdaExample.
Show where the bug happened:
traceback()
Tell us what version of XCMS you are running, the bug might be already fixed, or you could be running the (sometimes) unstable developer version:
sessionInfo()
If you found a solution, don't hesitate to sign up here and put it in the FAQ ;-)