The typical reason for "Forbidden" errors are due to mod_security being enabled.
mod_security filters information submitted to check for possible hack attempts and security breach attempts by the use of a set of pattern matching rules.
While mod_security is useful for preventing attacks, it is often overprotective and filters valid form information. If you receive this error, you should look into your Apache logs to find the rule that is triggering the error. With this information, you can ask your web host to remove the mod_security rule or replace it with a less restrictive rule.
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