This article provides a solution for the following error which maybe appear in AX 2012:
No metadata class defined for data contract object.
This error is caused by custom code and occurs after an upgrade from an older LAC version to 4.2.x.x.
To correct this, go through all your LACCustomCode one by one and change the code according to the picture below. The picture shows a sample from an older LAC version and from LAC version 4.2.x.x: