After upgrade of COM Proxy from Gen 7.0 to Gen 8.6, encountering this error running the CA Gen 8.6 COM Proxy which uses MQ to connect to the Gen server:
CSU-DLL-ERROR:(Sys-126) Attach to mqicf70n.dll failed in function CSUWin32Library::attach.
Release : 8.6
Component : CA Gen Run Time, Proxies
The COM Proxy is looking for a runtime file named MQICF70N.DLL which is a Gen 7.0 MQ communications runtime file that is loaded by Gen COM Proxy 7.0 runtimes.
The equivalent Gen 8.6 MQ communications runtime file is MQICFN.DLL i.e. it has no versioning.
Therefore, even though the COM Proxy has been upgraded from Gen 7.0 to 8.6, the COM Proxy execution must still be loading AX and CM dlls that were generated/built under Gen 7.0 rather than Gen 8.6.
It appears the old Gen 7.0 COM Proxy generated AX and CM dll files are still deployed and registered. They need to be unregistered followed by deployment and registration of their new equivalent Gen 8.6 versions.
That advice should apply irrespective of whether this is an IIS ASP COM Proxy or a VB program consuming a COM Proxy. If it is IIS based perhaps the unregister/register steps should be done when IIS has been stopped.
To check exactly what Gen runtime dll versions the AX and CM dlls are dependent on can be done by running the Dependency Walker program on them (depends.exe) which can be accessed from here: https://www.dependencywalker.com/
In particular, the CM dll will list more Gen runtime dlls than the AX dll.
NOTE: The MQICF*.DLL file itself will not be listed in the dependencies because the choice of communications runtime dll loaded is only decided at runtime via what is set for the transaction in the commcfg.ini file. However, other Gen runtime dlls will be visible which will confirm the version of Gen used at COM Proxy generation/build time.