I have an older trial version of Modscan32 from www.win-tech.com . It does not seem to connect with my MNET module. Why?

You need Modbus TCP client connectivity to be able to link to Prosoft MNET Servers for testing. Older evaluation or demo versions of Win-Tech's Modscan32 Modbus master simulator software did not allow use of TCP/IP Client connections unless you purchased the licensed version. 

If you have an older version, first, completely uninstall it. Then, download the newest trial version of Modscan32 from the www.win-tech.com site, install, and try it.

And remember, the software is not freeware. If you continue to use it, you should purchase the license.