I am grateful to you for suggesting the solution. I have used the ordinary Notepad software which is embedded in Windows ( I have Windows 7). It is still a mystery how I was able to open this file and there was a no mismatch at that time. And I could not open the same project/file after 2 days.
Roy Oestensen wrote:
Search for "source-language=" and "target-language=" in the file. They are almost at the top, so should be easy to find.
Ensure they give the correct language combination and save.
That will hopefully solve the problem for you.
Incidentally Notepad++ is a free utility, and much better than the Notepad version following Windows.