Had this unusual issue recently while deploying a Lync 2013 Enterprise infrastructure. All the Lync 2013 databases installed correctly, except for the rtcxds database, which is arguably the most important one. The generic error was system error 5: Access is denied.
"An internal error has occurred while trying to create or update the database."
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Weird. I have all the correct permissions. I am a domain and enterprise Administrator and a member of CSAdministrator and RTCUniversalServerAdmins (This was a Lync 2010 to Lync 2013 migration)
So I started looking around at permissions. Here's the file I cannot access via the C drive:
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And here it is via the C$ share – it's not even showing!
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I didn't screen capture the permissions, but I didn't have rights to view permissions on the file either. The same was true for the rtcxds log files as well.
The resolution:
Rename the rtcxds.mdf and rtcxds.ldf files to _old, and then reattempt installing the databases. This recreated the files within the CsData folder, set the correct permissions, and then the database install succeeded. Never did find a root cause for why this one occurred.