If you are installing Dynamics AX 2012 Enterprise Search, you may find the following errors in the installation logs “Error executing code: No system global variables”.  Depending on your SharePoint Farm configuration the
front-end servers can be configured with the BDC service running on both servers and cause the installer not to find the required DLLs in the global assembly cache (GAC).

To be able to install Enterprise Search under this type of configuration you will need to do the following steps:

1. Stop the BDC service on the second SharePoint server while leaving it running on the
   first server where you are running the Enterprise Search installation. 
2. After installing Enterprise Search on the first server, stop the BDC service on the
   first server where you just successfully installed it.
3. Move to the second server and start the BDC service and run the Enterprise Search installation there. 
4. Once Enterprise Search is installed on both servers, make sure both BDC services
   started and continue to operate using NLB. 

You can manage the BDC service from SharePoint Central Administration -> System Settings-> Manage Servers in FARM and click on all the front ends.  This information will be updated in the next version of the installation guides.