Speedlight problem

I have a D7000 that I use with 3 SB600 speedlights. I use soft-boxes that fit over the speedlights.
The speedlights are usually reliable and fire every time in the studio.
Today I had a shoot in a large aircraft hanger. All the lights had new batteries. All lights were "ready" and tested when pressed.
To my frustration, the speedlights would only fire if the camera was about 18 inches from the speedlight sensor. If I get in front of the light, nothing. If I get behind the light, nothing.

It's time for radio controlled flash synch.

Marcel, I don't understand.

When there is too much light around, the flash from the camera is not strong enough to trip the other ones. You can get radio flash triggers that rely on a radio signal to trip the other flashes. These work in broad daylight and even through walls.

Look here, there are many different models and they will work in full daylight.

Ahah! That's it!