...in Id3v23Handler.cs, which results in a NullReferenceException when any of these frames frame are found and unconditionally decoded on line 151 of the same file - is this perhaps an oversight when you were creating the portable version of Id3?
The problem frames are: TCOP, TFLT, TLEN, TEXT
Commenting out the addition of these frames makes everything work great. Also - you ought to consider adding symbols as outlined by David Ebbo here (http://blog.davidebbo.com/2011/04/easy-way-to-publish-nuget-packages-with.html
Patch file attached, thanks for the awesome library!