Problem with global variables in stored procedures

Hello, We have a system where stored procedures are used to modify data in tables and in some procedures we used global variables. The problem: sometimes Informix assign value to wrong global variable. In text stored procedure in 'Let' operator the one variable is used and assignment is made to another. We get trace of this procedures and see the wrong name of global variable. This effect is very rare and it seems to apear if two users execute the same procedures. We have this effect in two platforms: HP/UX 10 Informix 7.11 UC1 SCO 3.2 Informix 7.10 UC1 Does anyone else have this problem? Any ideas? Thanks, Oleg Tretjakov tov@inist.ru