ThinPro 6 (T7X60015) is only supported on the t628. Recommend to use the latest supported version ThinPro 5.2 (T6X52011) instead.
There will be a ThinPro 6.0.1 Version released very soon (T7X6010x) that also supports other units like the t520, t620, etc. but I would highly suggest when released to test it first as it now uses a 64-Bit Kernel.