Localization – translation

Hi!

I am trying to translate my site using Localization. It is only translating some parts. I do have this error message:

Warning: The actual loaded translation content contains mixed textdomains and is not pure translateable within one textdomain.
It seems, that there is code contained extracted out of other plugins, themes or widgets and used by copy & paste inside some source files.
The affected unknown textdomains are: theme-text-domain, tgmpa, option-tree

What does that mean and what can I do?

Thanks,
bjorn