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This is your problem in that message :
Unable to write to main menu.
When you switched you moved the files to a different machine?
if so some of your Directories lost thier permissions.
change all directories you had at 777 back to 777
Like the cache, templates_c, uploads and in some modules you might have had to make some directories to 777, recheck them or they might not work.
Then check the file
cache/adminmenu.php I think it should be 666
Hope this helps