Hi
Actually your 5m cable acts as antenna introducing noise on the data to from PC.
I once made an eprom programmer based on parallel port of PC and I had same problems, since I was short of time I solved the problem as follows:
1. I added 0.01 uF caps termination on the receiver side of the cable.
2. I used a sheilded cable.
3. made the cable as short as possible and problem was solved quickly.
4. I got some ideas from actual printers, seen how they made the interface.
5. I suggest you use line drivers and receivers, or differential amplifiers if you have to use the long cable.
Hope this helps
Regards
Mahmood