The company file you've selected is a BESTBOOKS company file...

Troubleshooting Alert Messages Overview > Alert messages (in alphabetical order) > The company file you have selected...
If you haven't already done so, we suggest you read the Troubleshooting Alert Messages Overview.

Situation: The company file you attempted to open is a BESTBOOKS company file, and can't be used by MYOB Accounting Plus in its present form.

Solution: Be sure the company file you attempted to open is the company file you want. If you're sure the file is correct, you'll need to upgrade the company file using the MYOB Accounting Plus Upgrade Assistant.