Windows 95 build 990

Windows 95 build 990 is a very early build of Windows 95 OSR2. It is referenced in the file  included with build 1009, which checks the Windows version and will error out if it is not running on build 990 or higher. This suggests build 990 was the first to include a functional implementation of the FAT32 file system.

You must be running build 990 or higher to use FAT32.