We have had a couple of other user reporting this problem. So far we are unsure why this is the case and the investigation continues. I have updated the bug report to include your details, which may help that investigation.
Would it be possible for you to try this older version of the tool. Some users have found that it does not give the error for exactly the same databases.
Unfortunately SQL Server 2012 is not yet supported by the tool. Are you able to connect to older versions of SQL Server? Assuming that you are, then it sounds like the development team need to take a look (and likely release a patch).
Looks like it worked after I created an empty database and script out all the tables that i need to mask to that new database. I then right click on the new database and open up the generator and it worked.