I used to date a guy who had that EXACT machine. I appreciate it's a popular model but it brought back memories.
Anyway, he made the shittiest coffee, real dirty-tasting brown sludge and I couldn't figure out why. When he wasn't about one day I tested the machine with some cheap supermarket grounds and I couldn't believe it: it was fine. Perfectly cromulent, surprising clean tasting, and hassle-free.
Anyway, after a while I figured it out. Turns out he was putting Nescafé instant coffee into the filter.