CU4 (SP1) upgrade to CU7 hangs on "Step3 of 11: Mailbox role: Transport service 54%"

It's all in the title.

CU4 (SP1) upgrade to CU7 hangs on "Step3 of 11: Mailbox role: Transport service 54%"

It's been stuck like this for over 30 mins, no special CPU or disk activities, memory load is normal.

Any ideas? (I want to post a screenshot but "

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"

I found that in "ExchangeSetup.log":

12/31/2014 07:39:23.0395] [1] The following 1 error(s) occurred during task execution:
[12/31/2014 07:39:23.0395] [1] 0.  ErrorRecord: The performance counter definition file D:\Program Files\Microsoft\Exchange Server\V15\Bin\Perf\AMD64\ADDriverCachePerformanceCounters.xml could not be found.
Parameter name: DefinitionFileName
[12/31/2014 07:39:23.0395] [1] The previous errors were generated by a non-critical task and will be ignored.
[12/31/2014 07:39:23.0395] [1] Setup will continue processing component tasks...
[12/31/2014 07:39:23.0395] [1] Executing (non-critical): 
new-PerfCounters -DefinitionFileName ServiceProxyPoolCounters.xml