This is usually caused by marine growth in the center board trunk. Does your Sandpiper sail in salt water? If so then barnacle growth can easily jam up the works.
I'd find a long, thin, flat tool (something like a metal ruler) to use to dislodge any marine growth around the center board and trunk. Mask, snorkel or scuba equipment would also help.
Sometimes going out on a 'bouncy' day (when there are waves) can be enough to free up a snag like this. Unfortunately this is this also the kind of day when you would want your center board deployed.
Thanks for the advice. I have been using a long saw blade to slide up around the keel. There is some blockage in some places, have not got them worked out yet. Not sure now if it is marine growth or something else. I have the boat up on a slip way but it is hard working on my back reaching up. I have now cut part of the top casing off and will try working down the top. I have tried pounding it with a sledge hammer but it still does not budge. I will keep working at it until I can eliminate all the blockages and hope that works but I expect that my sailing season is over before it started..