We are also encountering this problem. When first upgrading to MX 6.1 we found
this problem was occurring consistantly (verifying SQL Server datasources would
only work for the first few datasources then quite entirely). Once we updated
the JDBC drivers the problem seemed to be less frequent (I think it was to
version 3.3). Now we seem to encounter this problem once every few days.

I see that macromedia has just released DataDirect JDBC Drivers (version 3.4)
on May 13, 2005. Hopefully this will resolve the SQLServer connectivity
problem. Does anyone know if this is indeed the case?