It is a Student Edition ST6, which I've downloaded from here:
I have already tried to reinstall SE, nothing happened...
What version/license were your existing assemblies created in?
I have same problem on Solid Edge startup, but I have Installed latest MP & my solid edge started.
I am use Solid Edge ST8 & SEMP08.
Andrew however used ST 6 academic version. A MP may not be applicable in his case.
Dear have you check the following?
Turn OFF the UAC and the Symantec endpoint protection and check if solid edge works.