I know this message was a couple of years ago, but we are currently experie ncing the same problem. I found this thread hoping to find ways to get it unclogged and prevent it from happening again.
I won't say which brand of powdered dishwasher detergent it was (except tha t it was a major brand), but I stopped buying it because I noticed it was c lumping together, sticking to the sides of the dishwasher, and giving our d ishes a powdery-film appearance.
When the dishwasher stopped draining, I opened up the filter to clean it ou t and found huge clumps of the dishwasher powder all caked together...subst antially larger than the filter-holes themselves, meaning it clumped togeth er inside the filter itself.
(Doubters please note, companies can change their ingredients without notic e, get a one-time shipment of ingredients that are substandard or fake, and some ingredients have changed due to recent federal regulations...especial ly ingredients previously used to soften hard water).