Ok looks like you are making a new WTPart by a composite attribute correct? The addition of "<!--<Arg>{GEN:wt.enterprise.SequenceGenerator:WTPARTID_seq:3:0}</Arg> -->" should make a unique number but you might be limiting yourself. And Type, Subcategory and Object type make up the "3028A" portion? So does that WTPart by that number exist? Check the settings for that sequence to make sure its advancing properly. Be prepared for skips since it will keep moving regardless if there is a successful WTPart created or deleted. If you are ok with that, should work.
The one you are using is setup by the install for WTParts.
Based on the error message, it looks like its pulling a number 0000001501 first which would be the default OOTB OIR rule then trying to renumber it. Can you post the composite rule which merges all OIRs from the different levels. Strange that admin is able to do this but not users.