My Schedule Refresh Fails Occasionally

1) check your model calls, Power Query M code, tables loading etc if any its using that database for any reason, 

2) do the same check for your sql systema databse, if possible that database its a sub part that calls it for a extra information its stored there, if that the case just configure the access to it and done

for more help I recommedn you paste a little more detail about the case, theres a post that explain a good example of how to post questions for better asistince:https://community.powerbi.com/t5/Desktop/How-to-Get-Your-Question-Answered-Quickly/m-p/2336167#M843068