Does this error occur in some scripts or all scripts?
If this error is only thrown in some test scripts, then check the Formatting/Formulas in your excel sheet that you are importing. Most probably, it's your sheet that's breaking the DataTable.
I am sure excel file is not opened in the back , maybe Excel format causes it but I do not know.
This is the first time I am using function-library based framework for my tests and I have came up with this error and I solved the issue in another way.
-I commented all table readings from all functions
-I declared all variables as global with option explicit and Dim, in another function library called variables(this way is more secure than declating variables in libraries since QTP does not give permisson dublicate variables in different libraries)
-I called variables.qfl from all my tests.