You can dig through the trace log (should be under: c:\Program Files (x86)\BigFix Enterprise\BES Client\LMT\VMMAN\logs\trace.log, assuming it’s installed on Windows machine) but it’s not easy to find the error.
If you can’t find the exact error message in there, run a manual test via cmd (again assuming Windows machine) and see what it gives you back: vmman.bat -testconnection -config “<path_to_config_directo><name_of_connectionfile>.properties”
Generally speaking, the two most common issues are permissions and account passwords/expired passwords. I did see on one of the older VMWare hosts an issue propagating permissions where even though the account was given read-only on the root level, it didn’t propagate down to each nodes the same permissions, and it had to be added on each level before it started to work (some kind of ESXi permissions bug).
Hope this helps you.