thank you for your mail and sorry for the trouble. But the problem is not caused by our theme, it is your server that output a WARNING that it should not show. With your current settings all warning will be visible for everyone, means a hacker can provoke such kind of warnings and find weak points and hack your website. On public websites, those warnings should always be invisible, it’s only for the developer. The other thing is that your server does not cache the output, that’s why you cannot log in, also this is not up to the theme.
To solve it, there are two ways: contact your hosting provider and ask to turn PHP error messages and warnings off, and to set output_buffering on in the PHP.ini file. Second solution: we added a workaround to prevent the warning, you can download version 1.02 and install it, then it should work without any problem (I think it will be the fastest way…).