Hi Sebastiaan, hope you've resolved this issue by now, if not...
I understand this error is due to the frames being received out of order - possibly a hardware issue or flow control between the switches.
To confirm for Cisco switches FCoE is supported up to 7 hops (up to 3 of the switches can be FCoE switches), i.e. # of switches between your storage and host.
Hopefully this helps.
Cheers,
Grant.