You don’t need to uninstall the previous version.
Install the current dev version (same link as before) over your current one. Hopefully I’ve fixed the problems you have described above.
Be careful, if you remove all groups from you setup, you can’t re-add groups anymore, as this version will uses Joomla groups instead.
If you see joomla privilege settings in group tab in RP admin instead of old group list, execute the following SQL command:
INSERT INTO `#__raidplanner_groups` (`group_name`, `default`) VALUES ( ‘Guest’, 0);
replace #_ with your table prefix (e.g.: jos_raidplanner_groups)
Sorry for any inconveniences.