You might need to make sure you are running one of the latest updates, e.g. U77RC. Are you unable to run DBPro at all or is it just compiled exe files that won't run?
I don't know which update the free version is using. Does anyone know?
Edit
Just in case you missed it the latest U77 updates are available from the thread near the top of this board, i.e. see the first post in this thread:
U77 Public Release Candidate
Note in particular the comment under the heading Major Fix.
It is not yet finalised but is the best version to use if you are new to DBPro - and for most other DBPro programmers as well.