Conditional Formatting - Formula Problem?

I have a spreadsheet with a list of payments made against contracts. Columns A:D display contract_number, contract_value, Payment_date and payment_amount. In column E, there is a formula to sum the payments at each change of contract number: =IF(A2=A3,"",SUM(D$2:D2)-SUM(E1:E$2)). No big problems with this.

I have also applied some conditional formatting on column E to highlight when the sum in column E (payments) are not equal to the value in column C (contract_value): =AND(E3<>B3,E3<>"")

So, if the total invoiced against the contract (E3) is different to The contact value (B3) AND there is a value in E3, then apply formatting.

However, this doesn't seem to be working very well as several of the cells in column E have the formatting applied where the conditions are not being met.

Help appreciated.

Ken