Does the same error occur each time you try to update a plugin or this occurs each time with the same plugin?
]]>Weird. Have you installed any maintenance mode plugins?
I did a quick search and found another thread with a similar issue. Checkout the comment by @ktolliver and that should help both of you.
]]>Sometimes they will eventually install.
I wonder if it was how wordpress was initailly installed on the site?
]]>Do check if you have a file called maintenance.php either in the root director or in the root /wp-content/ directory?
It appears to me that there is some problem with that file. So remove the file (remember to backup the file) and try updating the plugins.
References:
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