Hi.
When you use backup-restore cycle, joomla engine can decided that some updates is not installed.
I mean that when I develop my extension, and need to alter database tables I do:
- folder
com_zhgooglemap\admin\sql contains all scripts to create/modify my database tables
- file install.mysql.utf8.sql - executed only one time when you install component (if you didn't have it yet)
- folder
updates contains all alters table/data when you update(upgrade) component.
When you upgrade component, joomla engine looks into updates folder for new files, and execute it. It caused table modification and new features appeared.
In your case for some reasons joomla decided that files didn't load and tries again execute it. In this case if columns exists in database table you'll get error about duplicated column, and installation stopped with error.
For example, you have the error
1060 Duplicate column name 'kmllayer' SQL=ALTER TABLE `tudqx_zhgooglemaps_maps` ADD `kmllayer` text NOT NULL;
TO FIX (for j.3.x version):
1 - get current version from JED
2 - unzip archive for j3.x
3 - open folder
com_zhgooglemap\admin\sql\updates
4 - find file with string
ALTER TABLE `#__zhgooglemaps_maps` ADD `kmllayer` text NOT NULL;
5 - clear this line, save file. DO NOT delete this file, we need it (despite the fact it is empty)
6 - zip it and install it. DO NOT UNINSTALL, just only install over exist installation. It means you upgrade component
7 - if you'll get new error message (about new duplication of the other column), go to #3, ie edit new file and again install
8 - after all this steps finally you'll get new installation, and joomla will know all, that all files in this folder is loaded.