The usernames and passwords that you used to sign in to data sources aren't up to date. In Power BI, go to refresh settings for the dataset. In Manage Data Sources, select Edit credentials to update the credentials for the data source.
Mashups between a cloud source and an on-premises source, in a single query, fail to refresh in the gateway (personal mode) if one of the sources is using OAuth for authentication. An example of this issue is a mashup between CRM Online and a local SQL Server instance. The mashup fails because CRM Online requires OAuth. This error is a known issue, and it's being looked at. To work around the problem, have a separate query for the cloud source and the on-premises source. Then, use a merge or append query to combine them.