Same problem here.
I was running HP customized 5.1 U2 and wanted to upgrade to 5.5 U1A.
I was forced to upgrade to 5.5 U1 ( not A ) because of this problem.
Everyone says that it's because some kind of bnx2 driver downgrade from HP in 5.5 U1A, but I really don't undestand that, because
Now ( 5.5 U1 ) I have
net-bnx2 2.2.4f.v55.3-1OEM.550.0.0.1331820 Broadcom VMwareCertified 2014-07-02
bnx2: net driver for VMware ESX
Broadcom NetXtreme II Gigabit Ethernet Driver
release-date : 2013-12-11T08:38:59.768585+00:00
And in 5.5 U1A there is :
vib20\net-bnx2\Broadcom_bootbank_net-bnx2_2.2.5d.v55.2-1OEM.550.0.0.1331820.vib
release-date : 2014-03-27T00:14:07.331201+00:00
I suppose 2.2.5d is greater that 2.2.4f ??
Or the letter is more important than the third number? anyway the release date is greater. Don't know what are the vmware rules.