I'm not sure what causes this one. Several developers encountered it in the past and where able to somehow solve it.
Can you post the builder logs?
How are you starting it?
If you are new to B4i or Mac then it is easier to start with the hosted builder.
I use the hosted builder, but today I helped to solve a similar error (not b4x software - other similar software) the error was my friend used the wrong certificate/profile when trying to compile in release mode.. the keychain can be changed in your mac
Mac is asking for a keychain password to access B4i in my Keychain