Incompability with tcomment

To the extent this is anyone's "fault" at all, it may just as well be tcomment's as UltiSnips's, so I posting this as a question. It is probably not a bug in either, but rather a coincidence.

When I have the brilliant tcomment plugin installed UltiSnips breaks. Simply moving the file tcomments.vim from ~/.vim/plugins to another directory fixes the problem. I have no idea what may cause this. The easiest would be to to simply install tcomment and see that happens; it is at http://www.vim.org/scripts/script.php?script_id=1173 . Unfortunately it seems Vim's homepage has some problems right now. To give you a taste, this is the beginning of the errors I get:

Error detected while processing function UltiSnips_ExpandSnippet:
line 1:
E31: No such mapping
Press ENTER or type command to continue
Error detected while processing function UltiSnips_ExpandSnippet:
line 1:
Traceback (most recent call last):
Press ENTER or type command to continue
Error detected while processing function UltiSnips_ExpandSnippet:
line 1:
  File "<string>", line 1, in <module>
Press ENTER or type command to continue
Error detected while processing function UltiSnips_ExpandSnippet:
line 1:
  File "/home/osse/.vim/ultisnips_rep/plugin/UltiSnips/__init__.py", line 621, i
n expand

Thanks for any help!