Ok you are H and I'm H so we should understand each others. So you opened the man page with ?`getSeq,BSgenome-method` as I suggested. Did you find any mention of an as.BStringViews argument there? The error message you got is telling you that there is no such argument (I admit it could be more straightforward about this, the meaning of "unused" in this context not being totally clear). You cannot make up new arguments and expect that they will just work. That's not how any programming language works (not just R) . BTW I don't even know what a BStringViews object is. We do have BSgenomeViews and XStringViews classes but AFAIK we don't have a BStringViews class.

Anyway according to its man page, the getSeq method for BSgenome objects has an as.character argument that you can set to TRUE in case you wanted the result as an ordinary character vector. Otherwise, you'll get a DNAStringSet object. If you want something else (e.g. a BStringSet object, but why would you want this?), you'll have to explicitly coerce the result to the desired class with something like as(..., "BStringSet"). Note that only coercions that make sense are supported. If you want a BSgenomeViews object, don't use getSeq(), use Views(genome, GRanges("Chr7:6000000-13000000")) instead.

Hope this helps,

H.