Endless "Your iCloud session has expired" messages - any solution?

I seem to have two related and incredibly annoying problems for which I have been unable to find a truly effective, long-term solution after extended web searches. Everything I try doesn't truly fix the problems, which I suspect are related ones:

1. In the course of normal usage of iTunes (ever since beginning use of iCloud), I frequently get the message "Your iCloud session has expired" and I am prompted to re-enter my password. When I re-enter it, everything works - until 5, 10 or 15 minutes later, when it pops up again - and again. I haven't been this annoyed since I dealt with the constant "Nervous Nellie" security popups on Windows XP. Is there any way to get iCloud to calm down?

2. Similar deal with iTunes Match. Almost every time I turn on any Mac with it enabled, iTunes Match will not actually work. I have to sign out from the iTunes Store, then sign back in, click iTunes Match, click "Add computer" (even though this is the same computer over and over again) and wait about 2 minutes to go through the activation and matching process again. Then it works fine. But should I close iTunes, shut down my computer, etc. and come back to use iTunes again, it's the same crazy routine all over again. Can't use it properly unless I sign out, sign in, re-activate iTunes Match, etc. Driving me crazy. Both iCloud and iTunes Match could be such tremendous services, but this buggy nonsense is hardly worth my time. Basically, a waste of $25 at this point.

Oh, by the way, iTunes Match works fine on my iPad 2 and Apple TV (never need to go through this song and dance).

If anyone has encountered either of these errors and found a solution, I'd be most grateful to hear about them.