I changed two things, and that seems to have fixed it: 1) I had been referring to the sproc up until today as dbo.xyz...., then this morning just before I posted the question here I changed it to SNBCO.dbo.xyz.... Both resulted in failures. As it turns out the correct path should be SNBCOReports.dbo.xyz.... At the same time as that mistake was corrected, the sysadmin also changed the settings on the server so that SQL Agent was no longer running in local mode (the sproc relies on a linked server in the query).

Certainly 1) had an effect, and perhaps also 2). D Lewis