Cannot resolve the collation conflict between XXXXXXX and YYYYYYYYY in the equal to operation

This error indicated that the strings in the join operation are from fields created in different collation. In general, it's better to recreate the fields with the same collation definition, but if you're just too lazy, and want to get things done, just cast to problematic field (in this example it's to 'SQL_Latin1_General_CP1_CI_AS'):

SELECT *
FROM A, B
WHERE A.F1 = B.F1 COLLATE SQL_Latin1_General_CP1_CI_AS