What Does: "Error in Materialized View Refresh Path" Mean?

I have a query and when I run it I can insert the results fine into the table it needs to go into.

But when we run it as an MV refresh:

dbms_mview.refresh(mv, atomic_refresh => transactional) ;

we get this error:

Error report -
ORA-12008: error in materialized view refresh path
ORA-01722: invalid number
ORA-06512: at "LINK_OD_IREPORT.R_MV_IN_PLACE", line 26
ORA-06512: at line 1
12008. 00000 -  "error in materialized view refresh path"
*Cause:    Table SNAP$_<mview_name> reads rows from the view
       MVIEW$_<mview_name>, which is a view on the master table
       (the master may be at a remote site).  Any
       error in this path will cause this error at refresh time.
       For fast refreshes, the table <master_owner>.MLOG$_<master>
       is also referenced.
*Action:   Examine the other messages on the stack to find the problem.
       See if the objects SNAP$_<mview_name>, MVIEW$_<mview_name>,
       <mowner>.<master>@<dblink>, <mowner>.MLOG$_<master>@<dblink>
       still exist.

Does anyone know what this means? I've tried querying these and it says they don't exist: select * from $SNAPSHOT_mv_name;

select * from MVIEW$_mv_name;