I guess, these errors are specific to german installation of vSphere 5.1U1a
first error: the username
No mather what the example in the ssl-environment.bat say, usernames are EVER written like „admin@system-Domain“ and „administrator@domain.local“. Names like „DOMAIN\User“ will not work and produce strange authentication errors.
second error: „Cannot reload the vCenter Server SSL certificates. The certificate might not be unique.“
I wonder how this error can raise on a fresh server, installed with „Simple Install“ (Build 1064983) and certificate requests generate by the script.
After hours of surfing the Web, I found this: http://communities.vmware.com/thread/446747?start=0&tstart=0
Open C:\ProgramData\VMware\VMware VirtualCenter\LS_ServiceID.prop and copy the line to clipboard.
Open C:\ProgramData\VMware\VMware VirtualCenter\vpxd.cfg and search for the line containing „<serviceId>vCenterService</serviceId>“ (line 50 on my file)
Replace „vCenterService“ with the GUID from clipboard like „{16B7163E-CCEA-47E3-891E-B2BFEEBEEB1F}:5“ (note the number at the end not missing „:5“ !)
Close and restart vCenter Service (can take up to 10 minutes to finish)
Now You should be abble to replace the vCenter Server Certificate.