I was trying to activate MapInfo using the offline email method. Now it asks me each time on startup for a response file from MapInfo 

Search in the start menu, "regedit" and open this tool.

Then navigate to -

Computer\HKEY_CURRENT_USER\Software\MapInfo\MapInfo\Professional\1700

Where "1700" is the version number of Mapinfo you are using.

Then delete the value -

ActReqPath