That Harris' polls are generally unreliable, or that the last one was in the 50s?
The former is my opinion based on experience, so you can either take it or leave it. The latter point I read in an article last night (which I am sure to be unable to find now) but give me a few moments and I can probably find it in another location...
In six out of eight polls, Bush's overall job approval rating remained in the 70s - the average was 75 percent - with the populists at the Democracy Corps showing him at 69 percent and the ever-outlying Harris Poll at 51 percent.