ProMdlSave returns PRO_TK_GENERAL_ERROR

Any idea why ProMdlSave returns PRO_TK_GENERAL_ERROR?

I have used
ProMdlInit, add a string parameter then check ProMdlIsSaveAllowed, ProMdlModificationVerify and if there is not error then I call ProMdlSave.

I have also tried with ProMdlnameRetrieve, ProMdlFiletypeLoad but same problem.

I also tried ProMdlDisplay before ProMdlSave but no gain.

Does anybody know why ProMdlSave gives General error?