Via the search function I found this info:
Creation of DVD files was not succesful:IFO Properties 6TCE The meaning of this error is, that CloneDVD has detected a structural inconsistency of the input IFO files. So far, this happened only if you try to post-process Instant Copy 8 files with CloneDVD. In case of interleaved/multi-angle titles IC8 produces invalid - so called VOBU maps - with duplicated and ... bad for fixing the IFO files on the fly ... missing reference entries. If this happens in any other situation, please don't hesitate to send the IFO files and a small bug-description to bugs (at) elby.ch. If possible, we will try to compensate these errors in future versions of CloneDVD.