You need to include the AGV library into your model:
File - Manage Class Library --> Tab Libraries
But it is available only until version 10 of Plant Simulation.
If you have also a V. 10 installation on your computer, then you can load the library using the context menu of the classlibrary in 10.1 --> Save/Load --> Load object. You will find the AGV library in the installation of Plant Simulation 10 Folder: Libraries - Standard - Free - Transport --> AGVS.lib
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