(Unusual) unresolved external

I'm getting some unresolved externals while linking a C++ project. They all look something like this:-

Quote:

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glibmm-vc80-d-2_4.exp : error LNK2001: unresolved external symbol "public: struct sigc::slot_iterator<class sigc::slot<void,struct sigc::nil,struct sigc::nil,struct sigc::nil,struct sigc::nil,struct sigc::nil,struct sigc::nil,struct sigc::nil> > __thiscall sigc::slot_list<class sigc::slot<void,struct sigc::nil,struct sigc::nil,struct sigc::nil,struct sigc::nil,struct sigc::nil,struct sigc::nil,struct sigc::nil> >::erase(struct sigc::slot_iterator<class sigc::slot<void,struct sigc::nil,struct sigc::nil,struct sigc::nil,struct sigc::nil,struct sigc::nil,struct sigc::nil,struct sigc::nil> >)" (?erase@?$slot_list@V?$slot@XUnil@sigc@@U12@U12@U12@U12@U12@U12@@sigc@@@sigc@@QAE?AU?$slot_iterator@V?$slot@XUnil@sigc@@U12@U12@U12@U12@U12@U12@@sigc@@@2@U32@@Z)

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Note the name of the file that's complaining (glibmm-vc80-d-2_4.exp). I'm used to seeing these errors from time to time but the problem file is usually either an obj file or a def file. I don't think I've ever seen this before with an exp file and I'm not really sure where to start looking for the problem. Is there some significance in the fact that this is happening in a exp file or is it just like any other unresolved external?

i.e. do I just need to find the relevant library to link to?