System.StackOVerflowException Occured In Mscorlib.dll?

I have two Datagridviews, Datagridview1 populates from and excel workbook the user selects. After that the user does a verification on the data. The Requirement I have is for the two grids to mark any records in yellow that are the same so the user knows what needs to be done.

I did the code to match the Cell Contents as there was no other way.Datagridview2 is the sartting point, the value in colum 9 is what needs to be found in Datagridview1 so i loop through the rows, colums by column, It finds the first lot and marks them yellow but then stops with the error. It does not run through all the entries.

My Sample code:'Button click event calls te public sub Datagridview2RowCounter

'Declare Current row position of grid 2

Dim Datagridview2CurrentRow as integer

'What text it should find and mark

Dim BookData as string

[Code]...

This is basicaly what i did but it stops after the 7th or so time it passes through all the code. I have more that 3500 rows of data to verify each time the workbook is opend, that is why i need to mark the Cells in yellow so i know what has been done.im stuck, everything works fine in the whole app, from importing data from excel into datagridview to the marking of other fields for some other reason, This is the ons that does not want to work.