error in core reports

Dears,
when I tried to make monthy customers sales based on customers
the report gives me wrong customer name after right customer name
in fact it gives me an item name instead of customer name
I may give you an example for that
name jan feb mar apr
client1 5000 300 200 5000
item2 5222 255 3222 6999
client3 9000 2323 223 1112
item4 5456 5465 5466 4444

so instead of customer name it gives me item name
although all numbers are correct

please help in that ASAP