Go CCIE Go!! - A Cisco Certified Internetwork Expert

I’ve been having a lot of trouble getting multilink frame relay to work. I’ve set my test lab up as follows R2 —DLCI 205— Frame Switch —DLCI 502— R5
In order to make sure I have the frame switch and DLCIs configured correctly I first configure simple frame relay as follows:
R2: interface Serial0/1 ip address 10.1.1.2 255.255.255.0 encapsulation frame-relay frame-relay interface-dlci 205
R5: interface Serial0/1 ip address 10.1.1.5 255.255.255.0 encapsulation frame-relay frame-relay interface-dlci 502
This works fine. R2 can ping R5 and vice versa. So now I convert the configuration to use multilink frame relay:
R2: interface MFR1 ip address 10.1.1.2 255.255.255.0 frame-relay interface-dlci 205 ! interface Serial0/1 no ip address encapsulation frame-relay MFR1
R5: interface MFR1 ip address 10.1.1.5 255.255.255.0 frame-relay interface-dlci 502 ! interface Serial0/1 no ip address encapsulation frame-relay MFR1
As soon as I type in “encapsulation frame-relay MFR1″ on the physical interface on each router the interface goes down and does not come back up: R2#sh int se0/1 Serial0/1 is up, line protocol is down
Just as an extra test I removed the frame relay switch from the middle and connected the two routers via dual back-to-back serial cables. I can get frame relay multilink working without a problem over the back-to-back cables.
Has anybody been able to get multilink frame relay working over a frame switch?

TIA,
Ash.