Oracle Stored Procedure Default Parameter problem

Hello,
I am receiving the following error when trying to call an Oracle stored
procedure inside of a package - PLS-00306 wrong number or types of
arguments.

This happens for several procedures within the package I am using and
by using DeriveParameters I was able to determine that the first
Default Null parameter in each procedure is not visible. The first
procedure has only one Default Null Parameter, the second has 3. If I
call either of these procedures without creating the first Null
parameter they work fine (the fact that the second procedure does
accept two other Null Default parameters has me perplexed).

I can access these without any problems from sqlplus, any ideas or KB
articles would be greatly appreciated.

Thanks,
Dave