it's not possible to call FM "DYNSQL_GENERATE_WHERE_CLAUSE" a second time

I need to call this FM several times in my report. Unfortunately then the error "FUNCTION_ALREADY_CALLED" is raised. The variable "FLAG_FUNCTION_ALREADY_CALLED" will be set to 'X' after the first call. How can I force a initialization of the variables of this function group in the calling program before I call the FM a second time ? Could anybody help me. Thanks in advance.

Best Regards Michael