I sometimes get this with my ABB ACS355 drive, it says in the manual that for single phase input models you need a Type A RCD also make sure your supply and motor cables do not run side by side. The drive may have an internal EMC filter, this can cause a leakage current to earth, in some drives it can be disconnected. It's usually best to disconnect all the VFD wiring other than the supply cables and try to energise from there, then begin to reconnect and retest as you go.