Iveco Brake Issues?

Hi,

I have an Iveco Cargo which is used as a horsebox. I've recently had a brake caliper replaced to get it through its test at the end of August (apparently it was leaking) and driven it about 100 miles since then without problem. Today the brake warning light came on, although the air pressure is fine and brakes feel fine. Please could someone confirm what the warning light is meant to indicate (I had thought it was just air pressure, but does it do more than this - e.g brake fluid level)? Any chance it is linked to the caliper being replaced? It had new front discs and pads and an overhaul of front and rear master cylinders in June time so they should be good. Is it safe to continue driving or should it be consigned to the shed?

Many thanks