Since a few days I am using the Pathogen plug-in together with the scripts from GitHub as described here. I think it is a wonderful way to maintain my personal ViM installation. However, after installing and trying OmniCppComplete I got the following error messages when attempting to complete something:

-- Omni completion (^O^N^P) Pattern not found

After a while I found out that the used complete-function ‘omnifunc’ was set to:

ccomplete#Complete

This is the generic completion function for C-based programs and does not work well with C++-programs. To fix this add the following line to .vimrc:

au BufNewFile,BufRead,BufEnter *.cpp,*.hpp set omnifunc=omni#cpp#complete#Main

This should leave you with a working OmniCppComplete plug-in managed from the vim-scripts repositories at GitHub.