There is no problem with having multiple identically-named events in a project if each such event is in a differently-named event folder. You can’t put them in the same folder, though, and Studio will stop you if you try, as we support users identifying events by their paths. In any case, whether they’re in the same bank or not is immaterial.
Certain versions of FMOD Studio contains a bug that would cause this error message to appear if you validated the project prior to building your banks. If you update to the most recent patch version of FMOD Studio, validate your project, and re-build your banks, the error should disappear.