If you have ICONVERT version 1.49 and want to run it under DOS 4.0 or 5.0.

First make a copy of ICONVERT.COM. (incase  you make a mistake.)
Use a Hex editor and go to address 53CA and you should find a 03.
Change this 03 to 04 for DOS 4.0 or 05 for DOS 5.0.