Transcripts are inherently stranded, so

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as strand does not make sense, and any tool has no choice but to refuse to deal with this. Work-arounds (in order of preference): • Find a better GTF. (Have a look at Ensembl; I have a GTF from release 108 lying around which only has

+

or

-

in the strand column.) • Find out what the strand should be and replace the

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with the appropriate symbol. • Remove all GTF entries without proper strand (this is especially appropriate if those entries are not meant to denote proper exons or transcripts anyway, but something else).

Thanks for you're help

Also point them here for support 🙂

Done