This may be an old post but I had the same issue and found a solution that worked. (I'm using Reason 5).
I had a song that would cause "out of memory" every time I tried to load it.
I patched reason.exe with the "4gb patch" (available at: http://www.ntcore.com/4gb_patch.php
Tried again on the same song, loaded just fine. The 4gb patch allows 32bit programs to access more memory.