could not find program unit being called

[ahmadsaeed]

Dear all,
we are facing a problem, your suggestions and comments will be very helpful here.
Actually what happens is that we are connected to oracle through forms 6i. suddenly we receive the error
" ORA-06508: PL/SQL: could not find program unit being called "
while doing some transaction.
we have searched on net and meta link. they say that the package / procedure called has become invalid or recompilation has occurred and that is not compatible.
Now we have monitored carefully that there are no changes what so ever has been made in the the package/ procedure.
what could be the reason behind this.
we have also checked the global variable issue. we use package level variables but declared in the package body only. (so these are not public)
what you say ?
Need your opinion.
Thanks
Ahmad Saeed

[stecal]

Was the fmb recently edited, someone deleted or renamed an existing program unit? Change in an attached library?