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The error_log are stored in different places depending on the hosting configuration. You will need to ask you hosting provider where those logs can be found. However, it may be a moot point as I have just release a new plugin update that should fix that error no matter where is was coming from.

As for the blue/blue folders, the wp-admin/css/colors/blue folder itself should be there and it should have CSS files in it, but there should not be another blue folder inside that wp-admin/css/colors/blue/ directory. The second lever blue folder is probably only a symlink to the first one, so that second one is all that should be deleted.