The above error is a security warning that recognises the file contains a macro and prevents you from opening it until you tell your browser to trust the source site. This can be hard to troubleshoot as non BrightWork tasks list will operate normally as their mmp files do not contain a macro. Following the below steps will help you resolve this issue quickly.
To add your site to the Internet Explorer Trusted Sites list:
Open Internet Explorer and navigate to your BrightWork site collection home page.
Click Alt on your keyboard.
Click Tools | Internet options.
Click theSecuritytab, then click the Trusted sitesicon.
Click Sites.
Click Add.
Click Close.
If you are still experiencing the issue after you can try project fix toolbox https://www.fixtoolbox.com/projectfix.html