ERROR: "The document '<walletname>' could not be opened."
This error message means that eWallet for Mac could not open your wallet file, however it can occur for several different reasons.
If you have copied your wallet from your iPhone or iPod using the Mac Finder to access eWallet's "File Transfer Mode", your wallet file may have the wrong permissions on your Mac. To fix this, click on your wallet file and press Command+I. Expand the "Sharing and Permissions" area of the Get Info window, and click on the padlock icon to make changes. Then, change your user to have read and write permissions.
The error could also indicate that your wallet file is corrupted.