To open an Analyzer project, you need two things, both of which were created when the project was started with the New Job dialog in the software. The first is the .fwt file which is the main file and where the completed tracking data will ultimately be contained. The second is the project folder. This will have the same name as you selected for the .fwt file (the video name by default) and contains the jpeg sequence and local work files. Both of these folders need to be in the same directory and share the same name for the project to open correctly.
If you are using Analyzer 2.0 or above, attempting to open an .impd file will not work. Analyzer 2.0 requires the .fwt file type.