Am I correct to assume that you get the error on the Summary before you come to the point where you are exporting it?
My guess would be that your dynamic columns result in exceeding the number of fields that can be handled internally. See the Help files, Appendix C for more information about that possibility.
I have hit the limit myself before now usoing a very large input source and duplicating all the fields to convert numeric codes to meaningful text..
The across fields are a bit unusual since in essence they derive from a single field. However I suspect that internally in the summary and certainly for export they have to be separated into discrete 'fields' which would then give you the problem. But is is a bit of a guess on my part and what you are actually doing may mean I am well off target.
HTH in some way.