Replication and Snapshots

This question is more Oracle, rather than MS SQL, related. However, I imagine a lot of MS SQL DBA's or developers like yourself are also familair Oracle, so maybe you can help me with this Oracle problem related to Snap shots and data replications.

When I'm in Oracle, I have had no problem when creating a datalink to another database. Everything returns properly when I am selecting a table from that datalink. However, when I tried to create a snapshot which selects from that data link, I always get the error message:
ORA-01422: exact fetch returns more than requested number of rows
ORA-06512: at "SYS.STANDARD", line 218
ORA-06512: at "SYS.DBMS_REFRESH", line 104
ORA-06512: at "SYS.DBMS_REFRESH", line 83
ORA-06512: at "SYS.DBMS_ISNAPSHOT", line 73
ORA-01403: no data found
ORA-06512: at line 1

Can you tell me what is wrong? Do I need to make any special configuration? By the way, the script that I have used to try creating the snap shot is:

CREATE SNAPSHOT "EDMSADM"."SNAP_STREET"
TABLESPACE "TWGIS"
BUILD IMMEDIATE
USING INDEX TABLESPACE "TWGIS"
REFRESH
START WITH to_date('01-Aug-2001 09:51 AM','DD-MON-YYYY HH12:MI PM')
NEXT sysdate + 7
WITH ROWID
AS
SELECT MAS.NAME FROM EDMSADM.MASTER_STREET@EDMS_TWORA1.WORLD MAS

Thank you very much for your help.