Upgrade addon from sap 2007 to version 8.8

Hello,

We want our module to upgrade the SAP 2007 Version 8.8.

we developed in vb.net in VS2008.

We've removed the DLL's sap 2007 and replaced it in the DLL version 8.8, both UI and DI.

The project was compiled, but there are places in the code that we receive an errors.

for example: string sUserName = oCompany.UserName,

it fails and can not pass the username to variable of type string.

The resulting error is:

"Unable to cast COM object of type 'SAPbobsCOM.CompanyClass' to interface type 'SAPbobsCOM.ICompany'"

We will be happy if someone could help us as soon as possible,

Thanks.