This error is caused by the user not having edit permissions on Purchase Orders in Dimensions.
To fix this:
Log into Dimensions
Click System, Profiles
Find and select the affected profile
Click Edit
Click the Purchase Orders section to expand it.
Click the Transactions section to expand it.
Select Process batch - POP Orders
On the right, ensure the Edit option is enabled. If needed, click Disabled to change it to Enabled
To save your changes, click Save.