  Several important cases of vector bundles with extra structure (such as Higgs
bundles and triples) may be regarded as examples of twisted representations of
a finite quiver in the category of sheaves of modules on a
variety/manifold/ringed space. We show that the category of such
representations is an abelian category with enough injectives by constructing
an explicit injective resolution. Using this explicit resolution, we find a
long exact sequence that computes the Ext groups in this new category in terms
of the Ext groups in the old category. The quiver formulation is directly
reflected in the form of the long exact sequence. We also show that under
suitable circumstances, the Ext groups are isomorphic to certain
hypercohomology groups.
