I was about posting a full guide incluiding this, but I think is unfair since I just changed some permissions.
So please, go on.
The exact problem it solved was the Errno 5, and I think it should work too with Errno 6.
Also, you could update the svn co svn://flashrom.org/flashrom/trunk@1846
flashrom to svn co https://code.coreboot.org/svn/flashrom/trunk@1846
flashrom , I don't know if you did it already.
And for anyone who need it, I have attached the update I used. XL2720Z V5.
It's compressed as rar instead of zip because of the size, sorry.