A lot of undefined variables errors

"Option Explicit"

If you specify that at the head of each asp page, it forces that error for any variable that isn't declared by a "Dim" statement before it's used.

It's a useful programming practice because it will catch any mis-spelled variables. Nothing worse than trying to figure out why something's not working only to find that you misspelled something. It's not required though, and many developers don't use it.

Some editors however, either have an option to insert it if it's not there, or insert it by default. So if you open up a file for editing then save it, you'll get that error for each variable with no Dim statement when it tries to run.