Several users have reported that they received the following error message when they launch iTunes and try to update iMatch running on Windows OS:
Please sign in again.
iTunes Match has encountered an error. Please choose Sign Out and then Sign In from the iTunes Store Menu
- Right click on your iTunes icon and click “Run as administrator.”
- When iTunes is running, sign out, then sign back in.
- De-authorize the computer, then authorize again (Store > Deauthorize This Computer and then Store > Authorize This Computer)
- Turn on iMatch
- Close iTunes and reopen without “Run as administrator”