Internal Server error (500 ) with all forms

All forms on my site produce an internal server error including the login, search and contact us forms. If I delete and restore the database or upgrade my drupal installation the error is fixed , but only for a short while and then suddenly without doing anything, the error reappears!!!!!!!!!!!

What i noticed is that when the site is working fine, the forms load quickly including the login form loading the stored username and password quickly. But when the error is there, the forms are so slow when loading.

I contacted godaddy , they took a look and said the error is not from their side.

I don't know what keeps bringing this error up and why do any updating to the database and files remove it temporarily.