Hi Howard,
Tell us a bit more - are you the facilities manager, contract cleaner, or sub-contract window cleaner to the office cleaners?
A non opening window on the sixth floor sounds a bit strange - is it the only one? Did the building used to have a cradle, because there's no way you can ladder that. You need to talk to someone there about how they used to get their windows cleaned, and get something done about the restricted access bit - is it a carpark? - because as Karl says it looks like you'll be needing a water fed pole to get that window done. How do the other windows at that height get cleaned, or are they only bothered about the boardroom?