misterious sequencing

I have the following DNA sequence which gives perfect forward result but the reverse is messy. PCR product is a sharp single band. Either gel purification or SAP-IT is used before sequencing reaction. Can someone here point out the key? Thanks.

TTATNNGAATATCTATATAATTGATACATATTTTAATTATAAAAACTTAAGTAGTATTAAATATTGATATTTCTTTTTGTACAAACCTTTGTTAGTAATTTTAGTTCATATTCAGTTATACATTGTTTTT
GGATGTTTATGCAATCTTATTTAAATATTTTAAAAATAATTGTAATATACTATTTTGAGCACATTTTTGTGTCTCATTTA
CTTTATTCATTTATCATTGTTATCGTCCTTAGGAAAACGTTATTTTCCTTATTTGGAAAATGGACATAATGAAAATTACG
GAAGAAAGTTTGTACAGGGTAACTCTGTAGAAGTTGCCTTCCTTCCTGGCTGTGGTCTTCCAAATGAGCAGACCACAGTT
ACATGTATGGAGAATGGCTGGTCTCCTCCTTGCAGATGCATCCGTGTCACTA