OK so found the Note 1243879 to a more or less similar problem like this.
according to it, the problem is based on the ECATTDEFAULT - also often found in the IMC TXT files.
Also, it says the problem might be resolved by updating SAP_BASIS 7.10 to a version above SP6. A possible solution but our SAP_BASIS is already at 7.40 SP6.
Any other thoughts?
(sorry I can't edit the start-post anymore for whatever reasons)