I have an epson 2200 and sometimes see the same thing. particularly when the printer hasn't been used for a while. I find that I can usually get mine working properly by doing a print head cleaning, from the maintenance menu, printing a couple of photos and letting the thing "soak" overnight. Ink seems to dry in the print head - a theory. I think that there are more drastic ways to clean the print heads, but I haven't had to use those.
the problems is that, it not over the whole sheet, just on very define areas ..... like an shape of an tree?? and the print has been use alot.... so don't think it is that
Doing head clean on epson 4800 iis very expensive to...... mmmm strange one???
thanks for your feed back