Microtek ScanMaker IIG User Manual page 217

Appendix B: Troubleshooting...
21 This message appears: "Not enough disk space."
Solution: You may get this error message if you try to scan an image larger
than the space available in your hard disk. Keep in mind that when
scanning into Photoshop, you need hard disk space that's 2 to 2-1/2 times
the file size of the image. In addition, Windows virtual memory takes up a
substantial amount of disk space to emulate memory or RAM, resulting in
reduced disk space for your program and scanned images.
Another situation in which this message may appear is when you use the
descreen function. With the descreen option selected (under the Filters tool
in the Settings window), you need a hard disk space that's 8 times that of
the image's file size. For example, to scan a 5-megabyte color image with
descreen, you need 40 megabytes (5 x 8) of available disk space. If you
turn off descreen, you will need a hard disk space that's 2.5 times that of
the image's file size (12.5 MB, or 2.5 x 8).
B-10 Microtek User's Guide for Windows