Magento login successful but

Login successful goes to account page.
Invalid security or form key. Please refresh the page. But that doesn’t help.
still cant goto dashboard or any page catalog , sales etc
can anyone help with this issue.
Its always worked in the past, im wondering if new fiver programmer did anything, so i have to go to him for help? As a couple of jobs ago he mentioned massive memory mail issue if i want to send group emails to all people, and then i have customers a week later, saying there not getting confirmations to there orders, seems a little odd.