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?
Release: WKLASE99000-11.3-Workload Automation-Agent SE
Component: Workload Automation Agent
Execute the command: cybagent -v
Example output of 64-bit Agent:
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
Example output of 32-bit Agent:
C:\Program Files\CA\WA Agent R11.3.4>cybAgent.exe -v
CA Workload Automation Agent for:
Microsoft Windows 32-bit
11.3, Service Pack 6, Maintenance Level 0, Build 946