I don't think there is a way to compile two different projects to one single one.
You will probably have to merge the projects by dragging and dropping.
So since you already did that, let's deal with the Audio error.
Did you put the Audio files exactly there where they have been before? With the exact same names?
Are they maybe in the "Files" folder instead of the "Sounds" folder?
If none of the above is the case, try to search for the audio events in the Event sheet and look whether the names are confused or something.