Dropped, -710 altered or renamed error when updating stored procedures

Periodically we get-710 (table has been dropped, altered or renamed) errors when updating stored procedures on a live and active database running with multiple clients (who are quite possibly using the sp at the time of the sp drop). Obviously, the relevant table has not consciously been dropped, altered or renamed directly by our changes. The problem, if it occurs at all, usually goes away once the prepared sp has been called by the client (presumably because the sp is forced to reoptimize itself). However, less frequently, the problem persists and the database server requires rebooting. At present, we are forced to drop all connections to the database before performing stored procedure updates due to the risks involved. Does anyone know why this occurs? I've seen related messages in the groups here, but nothing specifically to do with sp's. We have observed this problem on various instances of Ifx 7.31 -ian miell