Copied GP2010 and BP dbs to a new server, upgraded to GP2013 (successful) and then upgraded BP. Logged on to the BP site and it looked good except for a major issue. In the first screenshot you can see that I went to the home SP site - site actions - site permissions.
In this screenshot, I clicked onto the BP site - site actions - site permissions (site settings gives the same error) and goes to a generic SP error page about "file not found".
This error is so nebulous, I have no idea where to start given 90% of the upgraded site seems normal!
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