A database error occurred. The error message in the database was: invalid column name: x.CLIENT: line x col xx (at pos xx)" is raised when attempting to export master data using the "Export Master Data" app after adding a custom table in MDCMODEL transaction.

SAP Note 3724848 - MDG CMP - invalid column name: .CLIENT when exporting master data

Cause The default implementation uses 'MANDT' as the field name for active tables. However, if the message 'invalid column name: x.CLIENT' is raised, it indicates that the custom table is using 'CLIENT' as the field name.

Simpler Solution:

If the Custom Table is using MANDT field, Try changing to CLIENT

or if it is using CLIENT field, try changing to MANDT

Custom Backend Table Only.

The solution depends on the Version of the MDG Impleemntation (CL_MDC_DATA_BP)