This is a badly written error message from Make. It means “one of your filenames had a character that could be part of a regular expression”. Make is very naive about filesystems and quoting. It doesn’t believe that:
foo: 'The bar.'
refers to a literal string. It takes The as one word, bar. as another word, and then barfs on the period. Do this instead:
foo: The\ bar\.
or in your case, backslash to the period in .xcodeproj.