SQL2000, SP4, Enterprise Manager oddity

Last evening, our SQL server was rebuilt and SP4 was placed on it.  It had
been previously patched to SP3A.  Today, I can't make a call to a function
(that has been working for years).  I get an error message about needing to
use CONVERT.  However, previous views and stored procedures that use this
function continue to work as expected.  If I write the query in query
analyzer, the call to the function works as expected.

Could this be related to the install of SP4 or possibly the reinstall of SQL
that occurred last night?  Has anyone seen something like this before?