A common issue to those who work in SDLX Edit module environment is that you can not save .itd files when a segment in your left (source text) has the color green.
The reason is that your target segment does not have the right format applied.
To fix that you have to follow these steps:
1) click the paintbrush of the toolbar
2) highlight any of the colors on your left
3) highlight the text on the right that matches to the same color in the left
Repeat steps 2-3 until all colors in the left are applied to the right segment and the segment is no more marked as green.