Creating a Host profile gives error "Unexpected language"

Creating a Host Profile from a host gives on most of our hosts, but not all, the following error:

A general system error occurred:

 

See the error stack for details on the cause of this problem.

 

Error Stack

 

Call "HostProfileManager.CreateProfile" for object "HostProfileManager" on vCenter Server <vCenter Server Name> failed.

Error: Unexpected language: .

Does anybody have a clue how to solve this problem?

We are running ESXi and vCenter Server version 5.1 Update 1.