An error has occurred in a CRM .net customisation. Please contact your vendor to resolve.

On Sage 300 2019 PU1 and Sage CRM 2018 R3.

Within the Sage 300 Administration it allows me to Synchronise Tables and completes that without an error. However, when trying to import customers I get

"An error has occurred in a CRM .net customisation. Please contact your vendor to resolve"

If I try to "Promote to Sage 300", when I have entered a Customer Number that doesn't currently exist and then click Promote to Customer, the screen eventually appears with the Sage 300 Customer web screen, but the customer information then has to be manually put in and then saved.

I am using the Admin user with full rights, and I have allowed Admin WebAPI access. Updating customer information also works going from Sage 300 to CRM.

Any ideas would be appreciated.

Thanks in advance