This article describes a solution for the following compilation error that can appear in AX 2012:
System.Web.MimeMapping is not a class.
Lasernet needs at least .net version 4.5 in order to use the Attachment and loading of AOS / Client printers functions.
Please install .net version 4.5 or newer and then compile again.
Additional information on system requirements can be found in the Lasernet Connector for Microsoft Dynamics AX 2012 - Installation Manual.