It's possible that whatever process you are using to execute this BULK INSERT is running with a security context that doesn't have access to that particular share and/or folder. It is a different thing to run this kind of query from SSMS than to run it from SSIS, as with the latter, you can run a package a number of ways, and those different ways may all run with a different security context. For example, if this runs as part of an SQL Agent job, the the SQL Agent service account will need access to the specified share, whereas if you run this via SSMS, it's your logon credentials that wil be used.