I recently build a Citrix XenApp 6 deployment using RES Automation Manager but encountered problems with some (not all) installations. After a default installation the IMA service couldn’t start.  When looking at the eventlogs of one of those specific servers I found the following errors:

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Failed to load plugin C:Program Files (x86)CitrixSystem32CitrixIMASubSystemsImaAppSs.dll with error IMA_RESULT_WRITE_TO_LOG_FAILED

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Failed to load initial plugins with error IMA_RESULT_WRITE_TO_LOG_FAILED

and further on in the eventlog the following error was presented:

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When searching on the internet I found the following fix:

Well apparently this is a Citrix common item because the Citrix tech went straight to this registry key and changed it.
HKEY_LOCAL_MACHINESOFTWAREWow6432NodeCitrixIMARUNTIME

Then blanked out the following keys:
CurrentlyLoadingPlugin
ProductPlugins

After that, IMA magically starts and all services come back up and running.

So based on this I took one of the servers and blanked those keys:

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After this I could start the IMA service again and I was able to launch a published desktop on this server again.