PMDG 737 NG loses glideslope around 1500

I've done loads of searches for an answer both on this forum & generally online, but whilst several threads are close to what's happening, nothing unfortunately is actually answering the problem. I've flown the PMDG 737NG for years & the last couple of days something weird is happening. For ILS landings, I fly the approach correctly, once instructed by ATC I intercept the localiser and the glideslope & all looks well. I've got GS on the PFDS so I know it's all correct, I even if I choose to go for autoland, I'll active the CMDB & flare comes up on the PFDS. I've got the ILS frequency in both NAV radios, so all should be fine, but at around 1500ft everything disconnects, all indications on the PFDS go off & the plane climbs. I'm at VREF+5 on the MCP. I'm at a loss as to what's going wrong.

The worst thing is landing is my favourite part & you have go right back & start all over again to see if it will work, just for it to fail with the last 10 secs.

Can anyone give me any pointers as to what's going wrong?

I would have tried to post a screen grab, but fs9 has independently just frozen so I had to shut it down.

thanks

Pete