It looks to me your hosting has some issues. An error like this (generated by the 3rd party phpmailer class) should never happen (just like your previous problem shouldn't).
Combining this issue with the other problem it looks like a problem with too strict mod_security settings.
These strict settings will silently block php, form and/or mysql actions that it thinks are suspicious.
Ask your host to lower the level (or disable temporarily for testing) and try again.