Canon Rebel XTi/EOS 400D

spray a very very small amount of WD40 on the hings of pop up flash (use the thin RED spray tube)

This is a problem known by Canon, you will have to have it serviced.

Be aware that the built in flash does not pop up automatically in all picture modes. Try it when in the different modes (on the mode dial) and see what I mean. Does it popo up when manually opened ?, (small button on front left hand side of the viewing pentaprism/flash housing.)

mcomijohns. WHAT ARE YOU SUGGESTING!!!! Stop.

Lakshmy Be aware that the built in flash does not pop up automatically in all picture modes. Try it when in the different modes (on the mode dial) and see what I mean. Does it pop up when manually opened ?, (small button on front left hand side of the viewing pentaprism/flash housing.) PLease let u shave more information for a proper solution.

its disabled from the menu ...

Flash will automatically pop out only in AUTO mode, if the camera needs some additional lightning. In manual modes, you should use the flash button located at the left down side of the flash compartment, to manually force the flash to pop up

If the flash fires a full charge(eg. in a dark environment) then this message will appear whilst it recharges. If the message appears all the time and you cannot take a photo there is most likely a problem. Try taking some pictures without the flash card to eliminate that first.

Can you pull it up manually, Be careful when doing this but try opening it manually, it is possible that the catch for the flash is just stuck temporarily.

maybe it is dirty ... try cleaning it and the area around it ...

It appears that the small hook that holds the flash down is not latching properly and perhaps needs replacement. If your camera is still under warranty, call Canon Customer care. Even if the warranty has just expired (like 1 or 2 months), they generally honor it and get the service done free of cost.