What was your altitude? even at 15 degrees of dive depending on altitude it might not be able to compute. for the A-10, unless you are down low (<1000AGL) 15 degrees is a really shallow dive angle it could be the aircraft was unable to do its look-aside ranging properly if you were too high/shallow. Try pointing the nose 30-45 degrees nose low and you'll probably get a CCIP solution. If that doesn't work then I'd need to see a video or something to figure out what you're doing. CCIP doesn't care about your SPI, you should get accurate symbology even if your SPI is on the other side of the planet.
One other thought: were you in GUNS mode in the HUD vs CCIP with some other weapon profile called up? Its possible have the gun pipper in the HUD while you have CCIP rockets or bombs selected at the same time. It could be the CCIP INVALID was for the rocket solution or something... I'm just spitballing ideas what could cause it really.
Like I said, try getting lower/steeper with your guns passes and see if that helps. If it doesn't work then maybe theres some other switch error somewhere with EAC or LASTE.
