Hi AngelaDot
I'm surprised this has not been an issue in the past - as there have been plenty of forum posts about this. So while technically there is no limit, practically there is. Same applies with many things in MYOB, works fine until you hit some threshold.
I suspect that rather than being a function of the number of employees in your payrun, other factors also contribute, like the number of payroll categories used, whether you use leave accruals etc. Offline it seems to work ok even with large numbers, online (where it must be for MYOB's STP) is where users report issues and having to process payrun in small batches, as advised by MYOB.
What some users are doing to get around this is taking their file offline (permanently or just when processing payrun) de-registering from MYOB's STP Reporting and using STP Creator for STP Reporting. This software was specifically developed for offline MYOB users and allows them to comply with STP without being online to process payroll. It extracts the payroll data out of the MYOB file and performs all the functions of MYOB's Payroll Reporting Centre. The software even have a function to migrate from MYOB's STP and de-register. A side benefit is that payroll can now also be deleted, so if you make an error, you can delete and re-enter before you submit the STP Report to the ATO.
Regards
Gavin