Network connection from old application to SQL Server 2008 R2 lost once in a while
Axapta 2.5 was not supported on SQL Server 2005 or later versions so you are out of your depth there. To support later version of the database engine you will need to update the axapta application itself. 2.5 predates SQL Server 2005 by years: http://everything.explained.today/Microsoft_Dynamics_AX/

Any problems you have with incorrect statements are most probably due to the axapta server getting confused over the database version, you could try to change compatability level to 8.0 but I would recommend that you contact an Axapta certified partner and migrate to newer version of the application