Can you post a sample page?
One of the problems that could be happening is if you copy and paste text
from a program such as Word. A lot of people use fancy quotes and commas in
their documents, like the curly quotes instead of the standard quotes. These
aren't legal characters in HTML as they aren't a simple character code are
instead an embedded font type. What this means is, HTML doesn't know what
the heck it is so you end up with an unknown binary character in your page
which can be represented as a strange looking square, or simetimes as a ?.
If you try finding the comma in the HTML of the page in HTML view, try
deleting the comma that's there and just typing a regular comma in (again,
while in HTML view and not the designer). If this fixes the problem then you
know it's because of a fancy character insert.
Hope this helps,
Mark Fitzpatrick
Microsoft MVP - Expression