ECTR - unable to add documents under a folder - "Error converting field"

Hi All

When adding a document under a folder, ECTR get following error:

"Error converting field."

Document can be created within ECTR and document structure can be generate manually with TCode CV11.

ECTR Frontend Version:

5.1 SP04

SAPK-51004INECTR, ECC 6 Ehp8 SP02

Best Regards

Jimmy