Getting AppleScript error when trying to crop

[snowboardjoe]

I'm trying to crop video as I'm encoding it. I need to slice off about 50-100 pixels off the right side of the image. In ffmpegX I choose the crop feature to adjust for this. But any attempts to start the encoding process generates the following error:

AppleScript Error
The variable _sourcewidth is not defined. (-2753)

My values in the crop fields are 0 0 0 600. The original size is 720x480 and I want it to be 320x240 (or close to that).

Ideas or suggestions what's happening?

[Case]

I need to slice off about 50-100 pixels off the right side of the image.
My values in the crop fields are 0 0 0 600.

If you want to crop 76px, then enter [0,0,0,76].

[snowboardjoe]

I need to slice off about 50-100 pixels off the right side of the image.
My values in the crop fields are 0 0 0 600.

If you want to crop 76px, then enter [0,0,0,76].

Yep, I tried taking defaults, then went back to the crop box an entered as you indicated, but still get the same errors as soon as I try to encode the file.