Over the past 4 years I've seen this issue and it;s becoming a real pain for my customers.
If I go to:
Configuration->Virtual Resources->Virtual Storage Management and then choose a VIOS from the drop down I get a "Querying Virtual IO Server" pane (see attached). This runs and runs and runs and eventually times.
Initially I thought this was something to do with the VIOS scanning the FC devices but if I run cfgdev or vfgmgr on the CLI this runs successfully.
I can run all other functions from the GUI to VIOS without any issues so connectivity doesn't appear to be the problem.
The REALLY annoying thing is that sometimes it does actually work, but not very often.
Any ideas why this happens?