Hi @CCOMEAU 

Are you trying to change the ID of a customer, 

Can you check if the customer GI has “ Show delete Records “ enabled?

                                                  or 

See if you have below scenario for any customer 

AC-249083: The processing on the Prepare Data (BC501000) form failed with the Object reference not set to an instance of an object error if the following actions were performed:

1. A few stock items were synched between the Acumatica ERP and the BigCommerce store.
2. These items were added with the base sales price on the Sales Prices (AR202000) form.
3. A user prepared the Base Sales Price entity on the Prepare Data form.
4. The user deleted one of the items with the base sales price.
5. The user tried to prepare the Base Sales Price entity again on the Prepare Data form.

Fix Description: The Base Sales Price entity gets prepared successfully without a deleted stock item. If users then attempt to sync that Base Sales Price record individually for only the deleted item or items, the record or records are marked as deleted on the Process Data (BC501500) or Sync History (BC301000) forms.

HI @CCOMEAU 

Can you share the customer record?

Is the customer linked to eCommerce such as Big Commerce or Shopify?

Do you have any customizations that may be affecting that screen?

Hi @manikantad18

Yes I am trying to change the ID of a Customer, can you clarify what you mean by the Customer GI?

Hi @kandybeatty49

No the customer is not linked to Big Commerce or Shopify and there are no customizations. 

Hi @CCOMEAU 

If the customer has been deleted, you can not change the ID.

Is the Customer still in your system? If so, what is the actual customer status?

Hi @kandybeatty49 

Yes the Customer is still in the system and their status is active.

Hi @kandybeatty49

Thanks for your input you were actually on the right path.  The new ID that I was trying to assign to the customer had previously been used on another customer that had been deleted and Acumatica does not allow that.

Glad you figured it out :)