Ive had this exact same problem in the past and it ended up being static electricity blowing ink droplets around.
We bought a humidifier (because I live in a dry climate), and I bought the wide format kit from
www.stopstatic.com.
Also try a different roll of print media. Some brands have more static charge then others. I went from Arlon to 3M and had better results.
As far as cleaning the encoder strip. Use alachol and a lint free cloth and pinch the strip (gently) between the cloth and slowly and carefully move the cloth back and forth across the strip a few times. Or until the cloth comes up clean.