ESXI 5.1 on brand new DELL R520 purple screen

Hello,

We just bought a new Dell R520 and installed on it ESXi5.1 (custom ESXi install provided by Dell).

We constantly get purple screen with Exception 14.

Before the Exception 14 we got purple screen because we updated the VMTools, which apprently you should not do as there is a bug in ESXi 5.1.

We just switched from Hyper-V to VMware and I must say that even though there are load more features, the ESXi product seems not stable at all. Is this just my experience or is this common with ESXi 5.1?

Regards,

T.