Range Error on Extracting Pages

Need some help with the following code.  Everything works, ie export pages based on bookmarks with temp file names.  That is until I add code to go and export the file with the name of its bookmark.  Then I get the following error.  Any help would be appreciated thanks.

RangeError: Invalid argument value.

Doc.extractPages:7:Document-Level:test

This works

console.clear();

oDoc = this;
bkTrgt = []

this.bookmarkRoot.children.forEach(function(a){a.execute();bkTrgt.push(pageNum);})

bkTrgt.forEach(function(a,i,k){oDoc.extractPages(k,((i+1)<k.length)?k[i+1]-1:oDoc.numPages-1);});

This Doesnt

console.clear();

oDoc = this;
bkTrgt = []

this.bookmarkRoot.children.forEach(function(a){a.execute();bkTrgt.push(pageNum);})

bkTrgt.forEach(function(a,i,k){oDoc.extractPages(k,((i+1)<k.length)?k[i+1]-1:oDoc.numPages-1,oDoc.bookmarkRoot.children.name + ".pdf");});