Whenever I try to log into my website I get one of two error messages. One is "A critical error has occurred.
Exception has been thrown by the target of an invocation"  

or 

 "A critical error has occurred.Failed to load viewstate. The control tree into which viewstate is being loaded must match the control tree that was used to save viewstate during the previous request. For example, when adding controls dynamically, the controls added during a post-back must match the type and position of the controls added during the initial request." 

I contacted my web hosting company and they said it had nothing to do with them. However I don't know what or who else it can be. I have never had this issue before and don't know what to do about it. 

Thank you for your help in advance