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Try going to System > Modules and update your gallery module. I believe xcgal_index.html is one of the template files for one of the gallery modules. You much have one installed.
If that doesn't work, then reupload the templates folder for the gallery module you are using and try the update again.
Xoops is looking for that template file in the XOOPS database, but can't find it. Updating your module will should add this to the database.