No input file specified

When i try to login to wordpress i get a white page that says “No input file specified”. I noticed that if i go back two times in my webreader to wordpress index page and refresh that page then i can see the site admin. So then i am logged in to the system and i have to do the same thing when i logout.

However, i dont want to keep up like this so is there a fix for this problem??

Help appreciated

/Martin