I have no idea why you were able to import clips yesterday but not today. Are you at day 31 of your trial period (when many features become unavailable)? Are you trying to import the same clips, or ones from a different source? Here is a list of limitations of the
trial version.
Because many people want to work with 4K clips or want to do things to test out PD that the trial version doesn't allow, you may wnat to buy the full version to really get a sense of how the program will work on your computer, and take advanatage of the 30-day money back guarantee if PD doesn't meet your needs or expectations.
Please be sure to uninstall the trial version first, as it's different than the main program and can't be updated with a valid license key.