For me this happened when I was trying to run a program that uses JMS to connect to a Websphere MQ queue. The solution was pretty simple.
My PATH variable looked like this:
PATH="C:Program Files (x86)\IBM\WebSphere MQ\Java\lib;C:Program Files (x86)\IBMWebSphere MQ\Java\lib64;..."
The problem here was simply that the first MQ lib pointed to ‘lib‘ and not ‘lib64‘. So after I swapped the order of the paths
PATH="C:Program Files (x86)\IBM\WebSphere MQ\Java\lib64;C:Program Files (x86)\IBM\WebSphere MQ\Java\lib;..."
Everything worked again. Pretty simple solution but it took me quite a while to find it.
The Path variables were set by the installation program. I guess that if I had set them myself I would have seen it sooner but you never know. Sometimes you just can see the forest for all the trees 😉
Happened on Websphere MQ Server 7.0