When using web start you need to customise your configuration/JNLP file to allocate the right amount of memory for your users. If you have a particular user that can't launch Omniscope, you've set the memory too high. Reduce it a little until it works. If you really need the higher memory, create a different JNLP for that user, and advise they upgrade.

The memory option is here:
http://tc.visokio.com/webstart/

In the JNLP file itself, edit all cases like:
max-heap-size="750m"
and reduce the number.

It's most likely you've configured a number already which happens to be too high for a given user - for example, over 1100m is usually too much for a 32-bit PC, but rarely some 32-bit PCs require even lower figures, such as 800m.