Nested IF / VLOOKUP formula breaks when lookup value changes

Hi all,

I have a problem with a nested IF formula i am using in the worksheet 'Output' in the attached file. The result of the formula which i am querying appears in cell 'G9'.

The lookup value for the VLOOKUP formula is a concatenation of date and advertising campaign name, the result appearing in cell G16. In its current state the nested IF formula correctly looks at worksheet 'Turn' (the IF formula knows this by looking at cell C8), and returns the Total Cost value of £165.67 in cell G9.

The problem occurs when the campaign name - in cell B4 - is replaced with another campaign name (BE - Telenet - King Kong - Oct' 13 - DR). The lookup value in cell G16 updates automatically, but the VLOOKUP fails. I expect it to return the Total Cost value of £166.67 in cell G9, but instead an error is returned. As far as i can see the VLOOKUP should match with cell A3 in the TURN worksheet, and return the corresponding Total Cost value.

If anyone can tell me why this is happening and how to overcome the problem I would really appreciate it.

Thanks
Colin