try to update all BIOS and firmware prior to installing VMWare ESXi.
I think IBM/Lenovo even provides customized versions of ESXi which might help in that case, a quick search brought up this for example: Lenovo Custom Image for ESXi 5.5.0 Update 2 - BladeCenter, Flex System, Lenovo x86 servers, System x
We have many servers with IBM system X3250 M4 hardware and installed ESXi 5.5 without any issues. First we upgraded Firmware and installed ESXi 5.5.
for resolution see this thread and Dallo answer at third page:
if this doesn't resolve your issue upgrade your BIOS to the latest available version here:_________________________________________________________________________________________
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