Hi @Jon_Colman
You error looks like this, correct? Inside the red error dataset, expanded on the job information page (using the i-icon).
No destinations are available to fulfill request: toolshed.g2.bx.psu.edu/repos/iuc/kraken2/kraken2/.*
If yes, it is because the database is brand new at UseGalaxy.org and we are still adjusting the resources. Meanwhile, you can choose a different database or run the tool at UseGalaxy.eu instead. 
If no, and you are getting a different error, you are welcome to share back a share link to the error and we can review closer. Please see the banner at this form for How To or here directly. ā How to get faster help with your question
More soon about the known problem resolution, and thanks for reporting the problem!