I came across this error on a website
Wholesale Plumbing Supply and I couldn't print it anywhere. After I copied the source into Frontpage and fooled around with it, I found that there was a <frame> tag that was apparently useless. I previewed with and without, saw no difference, except that I could print (and received no error) without it. That was the problem in my case - an actual error in the HTML code, not necessarily caused by IE7 (although it probably conflicted).