When getting this error from 2015 P&ID and you have verified that you have a license available, try the following steps below.

1.  Go to your current P&ID support location, the default location is C:\CADWorx 2015\P&ID\System

2.  Do a search for *.bin to locate these system files NoProCheck.BIN & NoProCheck1.BIN

3.  Rename both of these file to include dash's/underscores in front of the name to make them unique.

4.  Now try and launch CADWorx P&ID Pro and see that you get a license.  

Note:  These two files are used by cad managers to control which users are on P&ID basic and who will be on professional.