STLink V2 missing from installation ?
Hello again, Stuart,
Of course, there could be a lot of reasons, which caused this error. I think, good starting point is try use general way to solve it:
Read this thread:
http://askubuntu.com/questions/378558/unable-to-locate-package-while-trying-to-install-packages-by-apt
especially answer of guy “Pandya” and try instructions there. Write here, if any additional errors happenes