Thanks for your reply's,

I thought it might be useful to upload the spread sheet the code is run from, unfortunately it is too large. I have copied some sample data into a separate sheet and attached it if it is any use in helping to get to the bottom of what is going on.

SampleData.xlsx

It would be great to get this running properly as I believe Macropod's code will be much more efficient to run than my own.

Thanks
Thom