Checkout Errors

[parma]

Hey, the site that I have been working on has been live since February. I have been contacted by many users of the site telling me that either when they log in it takes them back to the welcome screen or when they log in and checkout they are asked to log in once again. Is there any fix for this or anything I can tell the customer to do? I have told them its to do with cookies but am not 100% certain on this.

 

Would appreciate any help.

 

Kind regards