In my case, it turned out that the gauge wasn't tightened enough. I had two spunding valves with the Kegland Blowtie, but didn't use plumbers tape on either of the threads for the gauges. When I hooked it up to a keg in my kegerator, the gauge immediately showed the proper PSI but I heard hissing come out of it. Once I fixed that, it started working correctly.
It's still a learning process though. I have two kegs fermenting right now. For one of them, I seemed to have missed the boat since it took time to figure out the issue, then get the plumbers tape. It's only up to about 10 PSI right now, and it doesn't seem to be going up any more.
For my other keg, which started fermenting Sunday morning and started spunding Tuesday afternoon, I woke up this morning and it was over 50 PSI. I started turning the dial on the blowtie to release pressure and figure out where 25-30 PSI is, and after a minute I got some foam spitting out of it. Oops! I was on my way out the door and didn't have time to set up the blowoff tube again, so I'll see how it is when I get home later.