When he opened his to simulate the circuit, the components were nowhere to be found. The virtual lab was empty. Without the library files, Leo couldn't test if his address bits were matched or if his transmission frequency would hold.
If you cannot find a stable external download, you can use these functional equivalents that are usually included in the standard Proteus library: : A compatible substitute for the HT12E encoder.
: Unlike official models, third-party SPICE models may sometimes fail to simulate precise timing or "Valid Transmission" (VT) pin behavior correctly. Alternatives for Simulation