This error will happen when trying to build the DataMart. It may be related to one specific company and if you don't try to add that company you can still build the datamart.
This is a bug in MR. The field is coming from the user defined fields in your GL40000 (USRDFPR1, USRDFPR2, USRDRPR3 and USRDRPR4). In GP this field is case sensitive, meaning you can type in upper or lower case. However, the sort coalition in SQL is always case-insensitive for GP.. So what is happening is MR thinks when it builds the datamart that one of these fields is unique, i.e.:
Description
DESCRIPTION
are treated as 2 different unique records, even though they are really the same to the SQL Case Insensitive coalition.
To fix this, make sure all of your user defined fields are consistent, i.e. Description is the same in all companies, not Description in one and DESCRIPTION in another.
Remove the DataMart after fixing and re-add it.
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