I've been having problems with saving models in SW 2015 SP 3.0 for export to PTC Creo.  We have the Solidworks module from PTC, but it would not import ANY version of a .x_t file that I was able to save out.  V25, V19, etc...

It turns out that SW saves out a field in the header "APPL" which has switch from being "Solidworks" to "SOLIDWORKS" and the translator is case sensitive.

The current workaround is to manually edit the header and change the case to mixed case from ALL CAPS.

Another instance of where shouting just causes problems...