You might try Registering the file.
If you have Windows Vista :
Start/ All Programs/ Accessories/ Right-click on the Command Prompt and choose "Run as administrator".
type regsvr32 c:\windows\system32\ZLIBTOOL.OCX
at the resultant Command Prompt
Maybe uninstalling and reinstalling the software (what is it called, anyway)?
How to repair the operating system and how to restore the operating system configuration to an earlier point in time in Windows Vista