I have a Nikon D80 with 18-135 Nikkor lens. Everything was working fine. Battery fully charged. Now I can't take a picture. I just get a flashing "err" message and r11 code. Changed lenses - no difference. Any ideas?

Does the battery pack work? Leaving it on the charger for 24 hours shouldn't hurt the pack (too much) since the charger shuts off when the pack is fully charged. The most likely result would be a slight reduction in the capacity, but it should still work.

You shouldn't need to order another battery pack unless it no longer works.

You can reset the camera by using a paperclip and pressing the reset button

Try a diff lens on the D90 to see if its the body or the lens. Tony

Your motor may have gone bad. Try sending it to PhotoTech Repair Service in NYC. They are Nikon authorized, and can do the repair under warranty if you still have it. Also if you join they're facebook page, they will give you a 10% discount.
Here is the facebook page link, it has everything you need to send it in.
http://www.facebook.com/pages/New-York-NY/PhotoTech-Repair-Service-Inc/102527215194

Try sending it to PhotoTech Repair Service in NYC. They are Nikon authorized, and can do the repair under warranty if you still have it. Also if you join they're facebook page, they will give you a 10% discount.
Here is the facebook page link, it has everything you need to send it in.
http://www.facebook.com/pages/New-York-NY/PhotoTech-Repair-Service-Inc/102527215194

Please shoot in P mode. In P mode it will use the flash if you pop it up and not use it if it is down.

The flash uses LOTS of battery power. If you battery is weak the flash may take a long time to recycle (charge).

The Flash must be popped up and READY before you can use it. The flash is charged or READY when the RED light is on.

I hope this helps.

Yes, it will work just fine. I have this lens and my father has basically the same camera (D40) and it works just fine with this lens.

Check if the lens is properly mounted. If still you get the error message, clean the electrical contacts between the lens and the camera using an eraser. Take care not to let any dust fall into the body. Attach the lens and try.

Is the flash on Off mode? Is the battery fully charged? If not, charge the battery and try again.

Hello, please check your battery so it's fully charged. If it is maybe your memory card has some problems, or there are problems with the conections of the lens to the body (a gentle dry cleaning will probably do). If everything fails, check the troubleshooting section of the manual, or seek profesional help.