"There is no preview available"

Dear all,

here I am again with another question. This time the trouble is that I'm translating a .doc.ttx file but I'm unable to have a look at the target file in real time, simply because the preview window is all grey and it displays a message that reads "There is no preview available".  The preview function does work normally with other (non-ttx) files, though.

Thank you in advance for your answer.

Tomas