Well the logic of Computers..or Movie maker..or Windows more to the point..is questionable. I made a video ages ago and don't normally have trouble with Movie maker but this time I did, maybe to do with the length or graphical clips (I don't know if because I had lots of music and C.G.I. clips from Transformers Prime, it uses more power, resources etc) but it took me about a week to work out a solution, as in today I suceeded at last, having feared having to do the whole video again. If you experience a similar problem I can try to help you if you let me know, I can explain in whole detail, but basically Movie maker insisted I had missing files or corrupted in my project, they weren't and this was proved by exiting movie maker and loading my project again and it would randomly "decide" which ones were corrupt but regardless, it would never save as movie. So I urge you if you ever get a message about missing files to do check that you haven't deleted files used in your project but if you have checked that do NOT start your project again, you might be having the same issue I had and for some reason movie maker gives this wrong message, maybe because it can't handle all the clips even though it never says but that seems to be the issue. Not mentioning all the failed techniques I tried, today I cut down my movie into 3 parts, and had to make sure music stayed in place while doing so, then clicked the "Save movie" button, where movie maker converts your project into a movie, and 2 out of the 3 clips saved fine after waiting the long time it takes to save movies, which I am now used to having been through the process countless times this week, and for the other one, I just exited and loaded that part again and it saved fine. If your wondering why 3 parts, well I tried 2 of course as it's easier but movie maker failed to save again with the same error message which I will find and put on here in a minute to help others hopefully, and so I then split into 3 parts...and well the rest is history. So then I uploaded all 3 parts to youtube (I know it might not make sense but I had a feeling it might work as all clips from transformers in my vid came from youtube, so I theorised if I put my vid on youtube and uploaded it, then downloaded it again, it would be managable for movie maker, wether in terms of compatiblity or something else..dont know, yes it doesnt make sense because obviously its got the same large (271 clips!) amount of data as before, but it worked..), and downloaded those parts and put the 3 parts into movie maker, to once again combine into one project.. And..it worked. Phew! So Please check out my video if you want, here is the link,

http://youtu.be/B-izauiMmM8

And here is the error code in Movie maker to be wary of- "Sorry, your movie can't be saved. Find any missing files or remove the unusable items from your project, and then try again. Error: 0x87160129"

Again, some will say its codec problems and such and it looked like that way for me and maybe this problem has more than one solution but it might just mean movie maker "cant" handle your project, as in, it can but decides it doesnt want to, so a neat trick can sometimes work and I hope I can save you the hours spent looking for a solution as I spent ages on google and loads of other sites, trying out different things. See you soon :)