An alternative is to copy column A (with a heading) to a new sheet,
then apply Data | Filter | Advanced Filter to this column, choosing
Unique Records Only and Copy to another location (eg $C$1). Click OK,
then delete columns A and B.

Then enter this formula in B2:

=SUMIF(Sheet1!A$2:A$1000,A2,Sheet1!C$2:C$1000)

Adjust the ranges to suit, and copy the formula down.

Hope this helps.

Pete