Correct error message

flow/src/wWake.cpp

@@ -239,7 +239,7 @@ void Wake::connectVolElements(Tag *tagS, Tag *tagV, std::map<Element *, Element
         if (f->el1 == NULL)
         {
             std::stringstream err;
-            err << "flow::Boundary: no volume element from tag " << *tagV << "could be associated to surface element " << *(f->el1) << "!\n";
+            err << "flow::Wake: no volume element from tag " << *tagV << "could be associated to surface element " << *(f->el0) << "!\n";
             throw std::runtime_error(err.str());
         }
         svMap[f->el0] = f->el1;