Image Magick returns error numbers. Activate debug mode to get the full error message.
Possible causes of IM error messages:
1. You have a space in the path to the IM Convert utility. You must not do this. Windows users are advised to use a path without spaces, the short filename equivalent, or to set an IM environment variable and dispense with providing a path at all.
2. You have not set permissions for IM properly. Remember that the server must be able to use IM. Users of Windows IIS must give the I_ users (there are two) access the convert utility.
For all you out there wanting to install imagemagick with windows IILs you have to change the security settings on the cmd file c:\windows\system32\cmd.exe
you need to allow read access for the internet users. IUSR_computername
that will sort out the Warning: exec() [function.exec]: Unable to
fork problem