Is $scriptdir the same as d-tool\logo\ ?
Using $scriptdir within a script is the folder where that script file is located, but using $scriptdir from the channel editbox is the same as using $mircdir, so it's not clear where you were testing. Your post lists a relative path, which should work as long as $isfile(d-tool\logo\dtool.ico) is $true, but that's not the same as $scriptdir which always begins with the driveletter:\full-path
My tests with c:\windows\system32\shell32.dll shows that this is still working the same.