This is most likely a limitation of your host computer. Melodyne uses a great deal of processing power to load a file. Since it loads files into RAM, not having enough RAM to handle larger files can cause Melodyne to freeze. It is generally advisable to have at least 5 times more RAM available than the size of the file you are loading.

For example, if you load a 200 MB file, make sure you have at least 1 GB RAM free, above what your OS and applications will use. If your OS and applications (including Melodyne) are using, say, 300 MB RAM combined, then you will need at least 1.3 GB of total system RAM in order to properly load a 200 MB file. Also, keep in mind that polyphonic files will take up much more CPU power and RAM than monophonic files.

If you still have problems, even with sufficient RAM, you will probably need to break up the files into smaller pieces. It is best to work with files smaller than 100 MB, regardless of total CPU power and RAM.