Error On Join

The following query gives a list of users who have completed 0 modules. Code below:

SELECTpps_principals.name AS pname,
COUNT(PPS_SCOS.SCO_ID) AS coursecount
FROMPPS_PRINCIPALS
LEFT JOINPPS_TRANSCRIPTS ON PPS_TRANSCRIPTS.PRINCIPAL_ID = PPS_PRINCIPALS.PRINCIPAL_ID
AND PPS_TRANSCRIPTS.STATUS like '[PCF]'
AND PPS_TRANSCRIPTS.TICKET not like 'l-%'
AND pps_transcripts.date_created between '2006-10-01' and '2007-09-30'
LEFT JOINPPS_SCOS ON PPS_SCOS.SCO_ID = PPS_TRANSCRIPTS.SCO_ID
AND pps_scos.name like 'MT%'
WHEREpps_principals.login like '%score%'
AND dbo.PPS_PRINCIPALS.DISABLED IS NULL
GROUP BYPPS_PRINCIPALS.NAME
HAVINGCOUNT(PPS_SCOS.SCO_ID) = 0
ORDER BYpps_principals.name asc

This query works fine.

I want to be able to do another join to a table called EXT_USER_GROUPS to the query. This ties in the names to a group based on location. I have added this (see code below):

SELECTpps_principals.name AS pname, EXT_USER_GROUPS.LOGIN,, EXT_USER_GROUPS.NAME,
COUNT(PPS_SCOS.SCO_ID) AS coursecount
FROMPPS_PRINCIPALS
LEFT JOINPPS_TRANSCRIPTS ON PPS_TRANSCRIPTS.PRINCIPAL_ID = PPS_PRINCIPALS.PRINCIPAL_ID
AND PPS_TRANSCRIPTS.STATUS like '[PCF]'
AND PPS_TRANSCRIPTS.TICKET not like 'l-%'
AND pps_transcripts.date_created between '2006-10-01' and '2007-09-30'
LEFT JOINPPS_SCOS ON PPS_SCOS.SCO_ID = PPS_TRANSCRIPTS.SCO_ID
LEFT JOINEXT_USER_GROUPS ON EXT_USER_GROUPS.LOGIN = PPS_PRINCIPALS.LOGIN
AND pps_scos.name like 'MT%'
WHEREpps_principals.login like '%TEST%'
AND dbo.PPS_PRINCIPALS.DISABLED IS NULL
GROUP BYPPS_PRINCIPALS.NAME
HAVINGCOUNT(PPS_SCOS.SCO_ID) = 0
ORDER BYpps_principals.name asc

With this I get the following error:

Server: Msg 8120, Level 16, State 1, Line 1
Column 'EXT_USER_GROUPS.LOGIN' is invalid in the select list because it is not contained in either an aggregate function or the GROUP BY clause.

Any help appreciated.