Make a screenshot of the popup and post that.
Also, search your entire system for libavcodec.dll and let me know if there is another one than the one that sits with DGAVCIndex.exe.
Also, post a link to a fragment of a stream that causes this problem. Does it happen with the file test.264 that is included in:
http://neuron2.net/dgavcdec/dgavcdec100a2.zip