Hi,
My hosting provider updated for php 4 to php 5 and all my blogs started getting the same error you are seeing. Only on options.php
the other ones I could change like options-permalinks.php
Here is what they said happened, and what they did that fixed it for me:
It was because of a mod security rule, the techs removed the rule so you should be able to access it now
Contact your hosting provider to have them check into it.
