Hi @poora
This seems to be reporting a problem with the GTF file that you are using.
Specifically, the tool is looking for features labeled as exon in the 3rd field of the GTF file but didn’t find them. You might need to simply the format of the file you have, or you may need to source a different reference annotation file.
This guide explains how to source human reference data. → Reference genomes at public Galaxy servers: GRCh38/hg38 example
Please let us know if that helps or not. 