See: How do I setup the QODBC Optimizer? Where are the Optimizer options? 

The setting you need to configure is: For balances and stock quantities: the option "Nulls" - will return NULLs for all fields that cannot be kept in sync, "Dirty Reads" - means return the most current value that was loaded into the optimizer cache, and "Real Time" uses the slower method to get the data directly out of QuickBooks making sure you get the most current value for the requested fields. (Real Time is the very slow old method used in QODBC v6). 

You can also correct the Dirty Reads setting from within your connection string:-

DSN=QuickBooks Data;DFQ=\\Gt-server\company\QBEnterprise\qb9\GOLDEN TRIANGLE_for_QBE9.QBW;SERVER=QODBC;OptimizerDBFolder=C:\Program Files\Intuit\QuickBooks Enterprise Solutions 7.0\Components\QODBC\Optimizer;OptimizerCurrency=Y;OptimizerAllowDirtyReads=Y;SyncFromOtherTables=N;IAppReadOnly=Y

You should also switch off: SyncFromOtherTables=N as it makes QODBC very slow!