I'm no SharePoint wiz but I think the idea is that if you have permissions to open the document, the assumption is that it can be edited, thus the ability to check it out and lock it. As of 2013, apparently you can turn off requiring checkout, but you cannot disable the option to check out from being presented. The one exception I've read about was for pdf's and required you to add a custom key to the registry to disable it. Unfortunately, this would likely be a per pc user thing and frowned upon by IS.
- "doesn't work" is no help.Error #s/text do. State what's happening.
- Use code tags for code/sql; show where errors occur
Make all suggested changes in copies of your database or to its objects