MacSearch Issue
Have you Windows XP?
May be your system not full support PNG files.
That from Autohotkey's help file:
All operating systems support GIF, JPG, BMP, ICO, CUR, and ANI images. On Windows XP or later, additional image formats such as PNG, TIF, Exif, WMF, and EMF are supported. Operating systems older than XP can be given support by copying Microsoft's free GDI+ DLL into the AutoHotkey.exe folder (but in the case of a compiled script, copy the DLL into the script's folder). To download the DLL, search for the following phrase at www.microsoft.com: gdi redistributable
Also, try to put DLL into MacSearch folder.
Or convert all png to bmp format but rename bmp extentions back to png (not tested, the idea only)
Aqua-Soft Forums