I don't know what in particular Carrara may be objecting to, but the file might be corrupt. for example, a face that refers to a vertex that isn't present might do it.

Do you have any other programs that import OBJ? UV Mapper is a good one to try, it seems to be pretty tough to hassle with bad data, and it'll even fix some problems when you export it again. If you have a modeling program that might be good to try, too.

If you want to edit the file, one option would be to delete everything in the file except lines that start with a "v" (vertices) and an "f" (faces) and see if that imports. Depending on the file, you may need to try it with lines beginning with "g" (groups), in order to use the object. By doing that, you'll also be eliminating the UV coordinates for the object, so, if that does the trick, you may need to re-map it.

Do please make a backup before you edit the file, though.

Technically, the OBJ file spec also supports splines and some other goodies. I've never seen an OBJ that has those in it, but if they're there, I s'pose they could be confusing Carrara, too.