error

http://mytherapynet.com/secure/ - I'm getting an error message at the top: Warning: strpos() [function.strpos]: Offset not contained in string in /home/mtn2000/public_html/secure/wp-content/plugins/wp-super-cache/wp-cache-base.php on line 26 - I essentially want to use appointment, with membership and business portfolio - all with multi site. Each of my therapists at mytherapynet.com will have their own site - mytherapynet.com/secure/therapist_name - with their own appointment, their own member-only area for content.

my login is: http://www.mytherapynet.com/secure/wp-admin

please help me. Thank you. my account with you is mytherapynet. I just bought the yearly membership.