What does the error message "Scheduled refresh is disabled because at least one data source is missing credentials" typically mean?
a) The scheduled refresh function cannot run because the authentication details for one or more data sources are not provided.
b) The data source has been successfully updated, but the scheduled refresh needs to be manually enabled.
c) The refresh schedule has been changed, and no action is needed for missing credentials.
d) The scheduled refresh is disabled due to a temporary network issue unrelated to data source credentials.