Hi, go back to the run screen, click on 'Choose output to print' and make sure all yearly and average files are selected. If not, select them all and re-run everything (write inputs, run model, analyze outputs).
SWAT+ Check requires the analyze output step, so make sure that was done.
If you've double checked and re-run everything and you still get the error despite everything looking correct in the interface, you may have a model error that wasn't reported to the interface as being an error. Check your Scenarios/Default/TxtInOut folder and make sure the output files are there and populated. If not, the model probably had an error.