In UIDrawCall.cs line 292 there is:
#if !UNITY_3_5
string[] keywords = mMaterial.shaderKeywords;
for (int i = 0; i < keywords.Length; ++i)
mDynamicMat.EnableKeyword(keywords[i]);
#endif
But EnableKeyword is not available in Unity 4.1.2 so there's an error.
Of course if you don't want to support 4.1.2 that's your choice, but on Twitter you said you would drop support in the NEXT release, not this one

I have removed these lines for now.