The error might be reported during backup (Microsoft 365 sets protecting OneDrive accounts). The full error message is:

SPO: failed to get the lists from ( :    at System.Net.HttpWebRequest.GetResponse()

   at Microsoft.SharePoint.Client.SPWebRequestExecutor.Execute()

   at Microsoft.SharePoint.Client.ClientContext.GetFormDigestInfoPrivate()

   at Microsoft.SharePoint.Client.ClientContext.EnsureFormDigest()

   at Microsoft.SharePoint.Client.ClientContext.ExecuteQuery()

   at AsigraSharePointOnlineBLL_2013.Connect.ExecuteQuery(ClientContext _ctx, Boolean parseExceptionMsg, Boolean dontRetry, Boolean retryServerEx, Int32 lineNumber, String sMemberName).


The OneDrive account protected by the set reporting the error is no longer available online (that is, the user has been deactivated or removed).


Suspend the backup set (so that no scheduled backups are running for it) and keep it in DS-Client just for restoring historical data(if required).

If there is no requirement for restoring historical data, the set can be removed.