While exporting any dgn to Parasolids (.x_t format) this error message appears,This issue occurs when all elements present in that file does not fit in 1km size and thus it does not allow it to export to .x_t or XMT format. To solve this issue here is the solution by which that file could be successfully exported to XMT format.
In blank dgn file take that file (the file which does not fit in 1km size) as a reference,
After that lower down the scale of ‘Scale Reference’ which is available in the Reference dialog.In that way, the file be can easily be exported to xmt format. By this method scale and size of all elements in the Model, the file remained unaltered which avoids further size issues in future.