There are two different versions of the agent, 32 bit and a 64bit. Patches are version specific.
If you install a patch that does not match the type of installation the agent will not start after the patch is applied.
Its important to identify the version of the agent you are running to make sure you use the correct version either 64 or 32 bit.
How to verify if you are running a 32 or 64 bit version of the agent?
Execute the command
Example of a 64-bit agent installation <Please see attached file for image>
<Please see attached file for image>
C:\Program Files\CA\WA Agent R11.3.4>cybAgent.exe -v
CA Workload Automation Agent
for Microsoft Windows 64-bit
Version R11.3, Service Pack 4, Maintenance Level 1, Build 738
Release: WKLASE99000-11.3-Workload Automation-Agent SE