You'll need to give more information then. What SVN revision does SVN report you have, what environment are you compiling in (Linux, Cygwin, etc), what target are you compiling for, what patches have you tried to apply, what changes have you made?
The official sources don't have this error, so we need to figure out what you've done that is causing it.
To compile a plugin you'll need to add the plugin to the SOURCES file in the plugin folder as well as having it's c file present there.