There are many pitfalls here, e.g. the caps lock key (as VanityMemory already mentioned), the input method editor, using different keyboard layout languages, and just plain-old-typos. However, if there's something wrong with the wallet file itself, there are two ways you can attempt a recovery. (These are Windows-specific instructions; Linux will differ.)
Method 1 - restore from digital backup1. Open Armory and take note of the ID of the wallet you're having trouble with.
2. Close Armory.
3. Go to the Start Menu, click Run (or hold down the Windows key and press R -- on Windows 8 this is the right alternative).
4. Type this in the text box: "%appdata%\Armory", and then click OK to open the wallet storage directory.
5. Right click on the wallet file that has the ID you noted in step 1 (
and doesn't contain "backup"), and click "Cut".
6. Minimize your windows, right click anywhere on the Desktop, and click "Paste" to move your wallet file to the Desktop for safe keeping.
7. Open Armory.
8. Click the "Import or Restore Wallet" button (you'll have to wait until Armory reaches an "Online" state).
9. Choose the "Import Digital Backup" option.
10. Type this in the Filename text box: "%appdata%\Armory", and click the "Open" button.
11. Select the wallet file that has the ID you noted in step 1 (and
does contain "backup"), and click the "Open" button.
12. Click "Yes" when prompted.
If this doesn't work, you'll need to restore from your paper backup (you did print one out, right?
)
Method 2 - restore from paper backup(This method may not restore all of comments you've added to your wallet, but it should recover all of your bitcoin funds.)
1. Follow steps 1 through 8 above, if you haven't already.
2. Click the "Import or Restore Wallet" button.
3. Choose the "Single Sheet Backup" option, and then just follow the instructions.
If neither of these options work for you, there might be a typo in your password. There are tools that can try to search for typos in your password (e.g.
btcrecover), but they they do require some effort to use....
Let us know how this turns out (hopefully well!)