Common LaTeX Errors¶

Package reports "command already defined"¶

See http://www.tex.ac.uk/cgi-bin/texfaq2html?label=alreadydef

Error about symbol not existing in this encoding¶

This means you probably have the file encoded in something other than UTF-8. Fix that.
This means you probably have the file encoded in something other than UTF-8. Fix that. If you are using TeXStudio, then there is a little dropdown box on the bottom. Change it and re-save the file. Then go into Preferences and change it to use UTF-8 by default.