Hello,
According to your VisiLogic version, this PLC is quit old.
This PLC series have lower memory then the current products.
When you upgrade to a new o/s, there is incompatibility between this new o/s and the old hardware.
The latest version that supports old PLCs is VisiLogic V4.7.4.
You can download VisiLogic V4.7.4 swapper version from our web site at:
http://www.unitronics.com/data/uploads/VisiLogic_Software/Unitronics%20VisiLogic%20474.zip
Cheers,