I ran into this problem a few months ago, and had to install both SSMS and ERwin 4.1.4 SP 4 in order to reverse engineer a SQL Server 2005 database. CA added support for SQL Server 2005 with version 4.1.4, service pack 4:
http://supportconnectw.ca.com/public/erwin/infodocs/afmodsuiter414sp4-prodann.asp
I also had to request db_owner role in order to successfully reverse engineer some object types (stored procedures, default constraints, etc.) The db_datareader role was not sufficient.
The following link provides more detail...couldn't locate it earlier.