The Recipe Manager allows you to export your recipes in either its own format or a text format. When exported in the Recipe Manager format, it creates a .ckbk file. That file can only be read and opened by the Recipe Manager. No other program an open or read that file.
Export your recipes in the text format. You can then set up the recipes in a generic format that MasterCook can import. Follow these instructions: Importing Text Files.
Otherwise, you might try using RecipeClips. Visit their forum here. Post a message into that group asking if someone is willing to help you convert your recipes into the MasterCook format.