Debugging of L7: badrequest-select_conn

Dear all

We have a couple of erros in our logs:

kernel: L7: badrequest-select_conn [x.x.x.x:25899->y.y.y.y:80] (-1): GET ? /path/, 0 [hlen 299, nhdrs 9]

How do we have to read this error message?
Is this the exact HTTP message sent by the client: "GET ? /path/"
Then we would have a faulty client. Or is the question mark referring to something different?

Regards,
Grischa