I would like to suggest a more intuitive way to import a sequence of images, like a check box under the file type drop down box, to detect that the first selected image is from a seq of images, much like in After Effects.
Another good check would be to give the out the error message - Please take out the Period from the file name, and substitute it with {options} - or something to that effect.
Alternatively, do not allow Period to be a part of the filename, so its not an option at all.
THANKS !