(Event.o): In function
Event.cpp:(.text+0xacd): undefined reference to
Given what you have posted, it means that the function setBeginTime() of the Event Class, in the namespace com::egi::services::mff::api, has an argument of type EGIXStringWrap that belongs to the EGIBase namespace.
All is well till here, since the compiler keeps resolving after that line. We can deduce that the namespace EGIBase is visible to the library of the class Event.
Then, the compiler can't find a reference to getStringCopy, inside the EGIBase::EGIXStringWrap namespace, which is in a binary form (maybe a .o) expected to be built with a C++ 11 compatible compiler.
Given that my assumption is correct:
First of all, it is unlikely that you can do anything, given that those libraries are given to you already compiled, better contact their provider.
Secondly, getStringCopy is in the same namespace, EGIBase, so it must be visible.
Apart from that, I find it unlikely that the produced binary library is incompatible with a library of a previous C++ version (although not impossible).