Position following error on ACS806 + 57BL180D-1000 servo kit

Hello, some time ago I've bought an ACS806 servo drive and a 57BL180D-1000 servo from a chinese seller on Ebay, now I'm desperately trying to tune it using Leadshine's software "ProTuner" without any success.
I've downloaded ProTuner directly from Leadshine's website, the version I'm using is the ACS806 v.2.0 according to the manual (the drive's serial number ends with MS22B).
The problem is that I'm not able to lower the value of the position following error, it is always way too high, considering the manual, no matter what settings I change and if the speed reaches a certain value (527 RPM in my case) then it suddenly becomes unstable and the position following error increase drastically until the drive goes into alarm state.
I'm using a regulated 36V 400W PSU to power the system, it should be similar to the Leadshine ones.
What I'm doing wrong?

Thanks, Matteo.