Upgrade success but one custom report is complaining

[FWBB]

My upgrade went very quick and very smooth. Good job!
I only have one custom report that is giving me an error at this point.

##ERROR: Cannot open report Wrong OU or PC Name

In the report builder trying to preview the report i get the following error

Argument Data type int is invalid for argument 1 of substring function

I am sure I can rewrite the report but what has changed in the database schema to trigger this error

t-sql for the report:

Select tbladcomputers.Computername, tbladcomputers.OU As [Current OU], 
Case 
When SubString(tbladcomputers.Computername, 1, 3) = SubString(SubString(tbladcomputers.OU, 1, 6), 4, 3) 
Then 'false' 
Else 'true' 
End As [Name-OU not matching], tblComputers.Lastseen 
From tbladcomputers 
Inner Join tblComputers On tbladcomputers.Computername = tblComputers.Computername                     Where tbladcomputers.OperatingSystem = 'Windows XP Professional' 
And SubString(tbladcomputers.Computername, 1, 3) <> SubString(SubString(tbladcomputers.OU, 1, 6), 4, 3) 
And SubString(tbladcomputers.Computername, 1, 3) <> 'TRN' 
Or tbladcomputers.OU = 'CN=Computers,DC=us,DC=firm,DC=fowlerwhite,DC=com' 
And tbladcomputers.OperatingSystem = 'Windows XP Professional'

[Hemoco]

"Computername" is now an integer instead of the real computername.