The problem might lie in step 3 where you select the text. There’s no reason to select the text (it doesn’t contribute to creating the Text Image) and doing so changes the background color of the text (and sometimes the text color as well). When you click “Save” eggPlant generates the image using the specified properties and looks for it on the screen. If it’s highlighted blue or some other color and you didn’t specify that as a background color, then the text won’t be found.
There are other possibilities, but in order to analyze the issue, we would need to have a full-resolution screen shot of the SUT and the code that is generated for your Text Image. You would need to e-mail that supporting information to the TestPlant support e-mail address.