Quick easy fix for Insufficient Disk Space Warning When Attempting to Unpack and Install a Sage ACT! Update or Hot Fix. The error arises from the fact that the free space on the drive is a multiple of 4GB. The underlying issue is to do with a bug in InstallShield. To fix this create a file of 1GB, changing your free space available, to do so quickly, from a windows command prompt, on the drive affected run this command:

fsutil file createnew 1gbfile.bin 1024000 This creates a 1GB file. You no longer have free space that is a multiple of 4GB. Do the install, then delete the 1gbfile.bin file. More on fsutil on Technet.