We have heard from customers using WebSphere 6.0 and trying to use the v1.2 JDBC driver that they are encountering the above exception. This problem is primarily due to a name mismatch between our JDBC driver and another vendor's jdbc driver. While the v1.2 JDBC driver is supported by IBM WebSphere 6.1, it is not officially supported on WebSphere 6.0. We recommend customers to upgrade to WebSphere 6.1 or later when possible. If you are unable to upgrade to WebSphere 6.1 or later, one potential workaround is to install the v1.2 JDBC driver in a separate directory and configuring WebSphere to look for the driver in the new directory. We have seen this resolves the issue in a number of cases.
SQL Server JDBC Team