First check that the "database" metadata attribute is assigned to all inputs. This is the "database" short name for the reference genome build used for prior steps (mapping most likely).
Be aware that if you get the same error again, it could be that the database assigned is not indexed at the server you are working on. Is this the same server that you mapped the data on? It will be there.
If working on a public server that is different than the location where the mapping was run, using a custom reference genome, followed by promotion to a custom build, then assignment of that as the "database" could be the solution. Be careful to not introduce a reference genome mismatch problem.
If working on a local/cloud, adding the genome natively, indexing it, assigning as the "database" could be the solution.
Best, Jen, Galaxy team