Canon eso err 05 how do I fix it ?

 canon eos 400d  and just got error err05 the built in flash,s auto popup was obstructed ? 

This means a flash problem.

The reasons for it may be several ones. Let me go from the one with higher probability to the lower one.

1. Flash is stuck. It is the most comon reason, and more easiest to confirm. When pressed the shutter (or pressed the flash side button in P mode) you hears a repetetive click noise, and the flash won't pop up. If this happens, the flash is stuck.

Sometimes is solved when at the same time you press the shutter button, with the finger (or nail) you gently pull it up. Once is up, check for dirty, or any residues (such as tape glue, sand or something like that) that stucks the flash.

Some persons apply a thin layer of lubricant on the side hinges. Don't put so much lubricant or oil because will get inside the camera, and cause other problems.

2. If not click sound is heard, the either the flash actuator relay or the DC/DC board (that provides power to the flash board) or the flash board are defective. This can be confirmed only in a camera repair shop.

If you need further support, please let me know.

Best regards,