AF-ON with D50 need help, please

After reading so much about the advantages of the use of the AF-ON button to focus, I decided to give it a try.

It's cool and seems to have advantages, but I started to have an absurdly high number of blocking when I press the shutting button. Many times, camera doesn't allow me to take the shot and sometimes I have to use the switch of Manual focus to be able to shoot. In fact I missed some photos moments because of that

Does this happens to others or am I doing something wrong?

My configuration is:

• AF-C

• AF-ON button

• Dynamic area

Thanks for the help!

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Nuni