Thanks for the suggestions. Just in case you ever come across this issue Capita advised me to include Group Memberships (Historical) blue box in my report and under this select Group name. Now apply a filter to this field (using the red box on the right) as follows: Group type is Reg Group AND Active on is 5th Sept 2014 AND Group Name equals (prompt at run time). Now when running my Report I select an effective date in Sept and type the exact name of the new reg group (eg 2JO) and this works fine.