The exact error message is "Unspecified error" and it refers to line 1, character 36 of my code.
These are the very first two lines of my file:
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd
This all seems like a shady IE bug ;-) but I would like to make the error message indicator go away, if possible. It makes the customers uncomfortable...