Apart from the points of confusion mentioned in the earlier replies, you also need to be a little more specific about what you mean when you say you "can't reverse the process".

I know you mean that when you try to convert back from utf8 to UCS-2LE (a.k.a UTF-16LE), the resulting data file is different somehow from the original UCS-2LE data. But how is it different, exactly? Are characters missing, or added, or altered? Is the data corrupted in some way that makes it impossible for UC-2LE-based applications to read it or display it correctly? Can you pinpoint where the difference first shows up, and which particular characters are involved?

If you can look carefully at what the differences are, and update your post to include details about the differences you find, perhaps we'll be able to help you better.

(update: ... and it wouldn't hurt if you explicitly show what you tried in order to "reverse the process" -- it could be that if you tried some other method, it might work, but we won't know what to suggest if we don't know what you've tried)