SEPM updated with 64 bit virus and spyware , not updated with 32 bit. version 12.1.5 OS : 2008
Check This
Only 32 Bit Antivirus / Antispyware Definitions are not updating on the 32 Bit / 64 Bit Operating System
https://support.symantec.com/en_US/article.TECH122857.html
Run the symhelp tool on it for error checking
Troubleshooting computer issues with the Symantec Help support tool
Just to rule this out: Did you enable 32-bit content under Admin > Servers > Local Site > Edit Site Properties > LiveUpdate > Platforms to Download?