you must do a "make clean" because all jMax makefiles are broken regarding .h files.
you must rerun "configure". i recommend to do "make clean" after that.
CVS assumes text files in which it makes sense to merge file differences together. this normally results in update-conflict and corruption on jMax files.
Your previously working file is renamed as hidden file with a ".#" prefix. The new working file is available by removing the corrupted one and doing cvs update again.
The worst thing you can do is actually check-in a damaged file, in which case you'll have to peek an older version and check-in that file.