AWE is definitely enabled.

Adding the startup option -g512 should not be a problem, and I recommend that you try that. This is a quite common thing to do.

When this problem started to occur, had their been any changes to the server, like installing some new software or extended stored procedure?

Another story is that your entire server is somewhat antiquated. It's running Windows 2003 which has gone out of support, and SQL 2005 which is in extended support. And you are running 32-bit SQL Server. Wity 64-bit SQL Server, SQL 2005 or a later version, it is unlikely that you would have this problem.