Hi David,
Nothing really changed with regards to GEL startup functions and the OnTargetConnect() call between CCSv3 and v5. It pretty much works the same. It must be something else. Can you manually edit that memory location (via memory view)? It may be that GEL is having problems accessing that memory location in v5. If that works, could you try re-running the OnTargetConnect() call? You can do this from the scripting console:
js:> activeDS.expression.evaluate("OnTargetConnect()");
thanks
ki