Eletrolux washing m/c E50 code after replacing drive belt?

I have an Atrthur Martin (Electrolux) AWF1435 wahing machine (prod code 914517223). I suspected that the drive belt had either broken or come off.
Before removing cover I used the spin cycle to verify that the motor & pump were working, I could hear both.

To reset the belt I removed the top cover, detatched the water inlet hose, then placed the machine on its side to give access to both motor & drum pullies.

The belt replaced, I reset the machine vertically, replaced the water hose & top cover.
On testing (using the spin cycle) there was a clacking noise finally followed by an E50 error code.

Any ideas of what could have been upset in this process ?

Brian Boyes
May 2020