You know, the T key, shift, or space, or whatever personal setting you have to sprint. Why won't Origins even allow you to start the game until you remove it ?
You can still sprint by double pressing "W", so it isn't for the reason of a sprint exploit.

Why ? Double pressing W incurs an annoying delay before the animation kicks in, which leads to being bashed by a zed etc.

Are you playing on a server with sprint/turbo disabled?

Ah ok, I didn't know this was an option ? I just saw that the game won't let me play until I remove the hotkeys for sprint.
Why would a server disable such an essential feature ?

because you can "loop" it and sprint forever at full speed without losing stamina.
tbh thats kind of an exploit and some admins dont want that on their server.

And this exploit works only with the TURBO key and not with double press ?

with "double w" you can sprint for a few meters, after that you will lose stamina and run slow af.
if you hold the turbo-key and mash w you can run fullspeed forever.