I've got a very stupid and irritating bug, I was on a skype chat with some friends, and I uploaded my home mod, for them to test out. But now I'm on Skype and creation kit at the same time and I can't save my progress. This is the error I get:

MASTERFILE: Unable to complete operation due to failure removing previous file. Plugin 'Data\MODNAME.esp' may be locked or read only.

Temp file 'Data\MODNAME.tes' contains saved data.
''Yes to all'' will disable all Warnings for this context (this doesn't work)

When I completely close Skype and Save no errors appears and it works.

I don't think that's a bug. Usually, you're not able to save changes to any file that's being used by another program or user. You sent a file with Skype, Skype is using the file, so Creation Kit can't save.

How can I fix it??

Clear out your skype records with that user?

I agree.
Looks like the most probable solution.

This sounds like a Skype bug.

Fixed! I deleted all history! Thanks all!

Yeah this is a Skype bug. Skype does mark a file as 'no longer used' when it is done sending. It's really annoying and I do hope that they update Skype to fix this.