Too many serial number created in system, poor system performance

Dear Experts,

I have customer who needs to create 20,000 Serial Number per 1 GRN PO per month.

It takes her 10 minutes to auto-create the serial number and 20 minutes to add the GRN PO. During the time all users must be log-off, else SAPB1 will prompt run-time error.

Some old serial number in year 2009 and year 2010 will not be used again.

Anyone faces this problem before?

Thanks.

Regards,

Lay Chin