Thanks a lot Manu. I did not map the reads to the reference genome and got the bam files from other source. So, I do not know whether the data is stranded or not. Right now it is not possible for me to remap with TopHat or STAR. However, I tried with specifying 3 different library types to run cufflinks e.g., fr-unstranded, fr-firststrand and fr-secondstrand. Only fr-secondstrand gave me the FPKM values of gene, isoforms and transcripts. fr-unstranded gave error BAM record error: found spliced alignment without XS attribute and fr-firststrand was aborted and the last line was 7ffcbb0b3000-7ffcbb0b4000 rw-p 00000000 00:00 0 Aborted.
So, can I rely on the FPKM values of fr-secondstrand library type? Please let me know. Thanks in advance.