same thing happened to me, not once, but twice! Did the prep using Half-Lytely, which has always worked well in thepast. Took my pill, started chugging the liquid.... nothing! Finally I called the GI on call around 7:00pm, asking if it was harmful to keep chugging the liquid yet not going! I felt horrible, so full I sloshed when I moved. He said to keep it up, drink water, etc. I kept it up, things started a bit, but not like they usually do. Bottom line, it wasn't a good prep- had to schedule another scope in 3 months. So the next scope, did a 2 day prep with 2 bottles of mag citrate (which I actually like), then Half-Lytely. And 2-3 days of liquid diet beforehand. Same thing, I went.. but not enough! Poor prep.. my GI was able to suck out enough liquidy stool to get some ok biopisies, but it was still considered to be poor prep, clinically. The stool was all liquid, but it wasn't passing. My colon has gotten pretty thick, due to scar tissue, which could be the cause. And it's not that flexible these days either, which doesn't help.. Anyway, I'm due for another in January, and have already started to dread it. I plan to drink some mag citrate, then do the prep, and also go on a liquid diet for like 3 days prior. Sometimes, they just don't do the trick! And they tell you to drink water too- I'm so full of gross prep I can't swallow anything! Are you doing a re-scope soon? I felt like such a failure.. haha!