It appears that Apple dropped support for certain formats of legacy bitmap graphics in OS X 10.13 High Sierra. form•Z 6 uses this format for some of its palette graphics. To fix this you will need to replace the resource file in your current installation with a new one that contains updated graphics that are supported by OS X 10.13.
Please follow these Steps:
• Be sure that you have form•Z 6.7.3 installed. This fix will only work for form•Z 6.7.3. If you don't have it, you can download it here: www.formz.com/update
• Download "formZ_RenderZone_Plus.rsrc.zip" below if you have a form•Z RenderZone Plus installation or "formZ.rsrc.zip" if you have a regular form•Z installation. If necessary, extract the zip file. You should now have a file named “formZ RenderZone Plus.rsrc” or "formZ.rsrc".
• Locate your formZ 6.7.3 Application folder (Usually in Applications/formZ/)
• Right-click on the "formZ RenderZone Plus" or "formZ" application icon and select "Show Package Contents" from the menu.
• Open the "Contents" Folder.
• Open the "Resources" Folder.
• Replace resource file in the "Resources" Folder with the one that you downloaded.
• Launch form•Z 6.7.3!