|@Matt123, that's not what the problem is, the < and > are ok because they are enclosed in quotes and so they don't get treated as redirection characters.|
The problem is you are trying to delete a substring from within a line. Batch is not very good at doing that. You may find it easier to write it in VBScript, or use a helper utility such as sed (available from GnuWin32).
Also, you are assuming all your text within the < s > and < /s > is on the same line. Is that a valid assumption? In html, it is allowed to span any number of lines.