In Digimon dusk trying to train Digimon but it wont let you train it. Can someone help

Check your Digimon's Apitude, the stat that only increases when digivolving and degenerating. This stat determines the max level your Digimon can go. Poyomon has an apitude of 10. That means Poyomon can only go to level 10, unless you digivolve it into somethig it can digivolve into and then degenerate it. Then Poyomon's apitude will be higher, letting it level up more.