After updating a number of my sites recently, I was greeting with an error stating "The server tag is not well formed..." on a number of pages. One of the applied patches was
MS07-040 which does fix some asp.net issues, but I didn't see where in the code i was doing anything untoward. After drilling down to the code itself it turned out that I had a tag that was using localised resources, but instead of using the "ResourceKey" attribute, mine said
"ResourcêKey " (note the funky "e").
Previously this hadn't been apparent as all it meant was that that field kept it's default value and didn't use the intended resources, but since the patch it causes the error. My guess is that to fix the null byte termination issue, Microsoft has reduced the list of allowed characters in tag declarations to a restricted set (probably ANSI) - i've seen other reports similar to this where code contained ״ rather than " .If you get this error after patching your servers, be sure to look out for incorrect character usage.