Here's a good rule of thumb to keep in mind when you encounter one of the issues above: Something is not right. Not to oversimplify, but if you are able to perform some functions in L2L, say on one line, or module, or machine, but not in another line, module, machine, schedule, user record, etc., look at the setup of the working item vs. how the non-working item is set up.
Here's a commonly reported occurrence. Someone has an Admin level account in L2L. There are functions that they think they should be able to perform. However, when they attempt to access or edit a page, they are unceremoniously kicked back to the login page.
The first step you should take to troubleshoot this issue is to look at the account holder's setup in their User Profile. Having an Admin account does not automatically mean full functionality to every possible transaction in every module throughout L2L.
If the desire is for this person to have full Admin access and privileges, make sure they have the module specific permissions. This is as easy as simply looking at the Administrator Security Settings: Setup => User Setup => Administrator Security Settings
This is almost certainly the case, whether you're talking about Line Cycle Times, Shifts, templates, scheduled reports, thresholds, etc. If it can be set up in L2L, something can inadvertently be set up differently. I would estimate that 97% of the time, when we hear that something isn't working correctly, an expected radio button "Won't let me click on it", "The hyperlink doesn't take me anywhere.", "My selection is greyed out.", that tells us that something in the setup isn't right.
Especially when immediately followed by, "This is the only line where this is happening." or, "I can see this and do this everywhere else. It's just this one _ _ _ _ _."
It can take a minute to find the discrepancy in the setup. It takes a little bit of digging and a little bit of comparing. Here's what we do and how you can diagnose the problem more quickly: Open the details pages of the items you wish to compare. If at all possible, utilize an extra monitor or two, so you can compare the screens side by side. If you don't have an extra monitor at your disposal, try capturing a screenshot or snippet of one page, and display that next to the other page. Be sure you're using a known good (i.e., working correctly) setup alongside the problem child.
You will encounter this on all websites and all applications, so don't let your frustration get the better of you. Just take a few minutes and try the suggestions above. You'll probably find it faster than you thought. And this is the best way to ingrain the lesson. When you find it, be sure to share it with your teammates. That will further reinforce the learning experience!