Poweredge 1550 and IBM ServeRAID 4Lx

I'm having booting problems with a ServeRAID 4-Lx controller in a Dell PowerEdge 1550. Controller is properly seated in a PCI64 slot. After powering up the machine the serveraid BIOS pops up and reports "1: ServeRAID-4Lx Slot 2, power-on self-test takes up to 3 Min(s) 0 Sec(s)". This timer doesnt count down, and even after 5 mins nothing happens.

I've tried both PCI slots, tried several BIOS versions on the Dell machine, to no avail.

Tried the card in 2 other machines in PCI32 slots, and one of them had similar behaviour as the Dell machine ("power-on self-test takes up to 3 mins" and then nothing), and the other machine did pick up the card correctly. On this machine i've booted the most recent ServeRAID support cd (5.11) and the controller firmware and BIOS was succesfully updated from 4.84 to v5.11.

Retried all tests with the new ServeRAID BIOS and firmware 5.11, but the same situation persists.

Also tried various poweredge 1550 BIOS revisions to no avail.

I've had a similar issue with a ServeRAID 4Lx on a SuperMicro 370DLE motherboard, but was able to solve it in this case by upgrading the motherboard BIOS.

IBM techsupport could not help me with this issue, so this is my last resort.