At first I was trying a script I wrote, but when I had problem with that I tried the examples in their tutorial. For instance, after copying their simple-unsharp-mask example and saving it as script.scm in the .gimp-2.6\scripts\ directory, when I try this:
gimp-2.6.exe -i -b '(simple-unsharp-mask "0000.bmp" 5.0 0.5 0)' -b '(gimp-quit 0)'
I get the following:
GIMP-Error: Opening 'c:\Program Files (x86)\GIMP-2.0\bin\5.0' failed: No such file or directory
GIMP-Error: Opening 'c:\Program Files (x86)\GIMP-2.0\bin\0.5' failed: No such file or directory
GIMP-Error: Opening 'c:\Program Files (x86)\GIMP-2.0\bin\0)'' failed: No such file or directory
GIMP-Error: Opening 'c:\Program Files (x86)\GIMP-2.0\bin\0)'' failed: No such file or directory
batch command executed successfully
batch command executed successfully