Hi, I am using a typical ucsc gtf file downloaded from the ucsc genome browser, btw getting an error for invalid file format in gtf file looked at the test file, my file looks ok.Pls see below 
#name	chrom	strand	txStart	txEnd	cdsStart	cdsEnd	exonCount	exonStarts	exonEnds	proteinID	alignID
uc007aet.1	chr1	-	3195984	3205713	3195984	3195984	2	3195984,3203519,	3197398,3205713,		uc007aet.1
uc007aeu.1	chr1	-	3204562	3661579	3206102	3661429	3	3204562,3411782,3660632,	3207049,3411982,3661579,	Q5GH67	uc007aeu.1
uc007aev.1	chr1	-	3638391	3648985	3638391	3638391	2	3638391,3648927,	3640590,3648985,		uc007aev.1
uc007aew.1	chr1	-	4280926	4399322	4283061	4399268	4	4280926,4341990,4342282,4399250,	4283093,4342162,4342918,4399322,	NP_001182591	uc007aew.1
uc007aex.2	chr1	-	4333587	4350395	4334680	4342906	4	4333587,4341990,4342282,4350280,	4340172,4342162,4342918,4350395,	Q548Q8	uc007aex.2