In a Router running 12.4(20)T version and trying to install Anyconnect .pkg file through SDM 2.5, you will receive an error message as follows
"Error installing package: Unknown Error. This maybe occurs if your router uses a LEFS file system. Converting it to a use a DOS files system may resolve this issue."
This issue occurs due to the lack of support for anyconnect package in SDM 2.5 and hence the warning. Use Cisco Configuration Professional (Cisco Configuration Professional (CCP)) 1.2 and above to install the .pkg file. It has the similar device manager support as like SDM.
CCP is a GUI-based device management tool that allows you to configure Cisco IOS-based access routers, including Cisco integrated services routers,Cisco 7200 series routers, and the Cisco 7301 router. CCP is installed on a PC and simplifies router, security, unified communications, wireless, WAN, and basic LAN configuration through GUI-based, easy-to-use wizards.
Routers that are ordered with CCP are shipped with Cisco Configuration Professional Express (CCP Express) installed in router flash memory. CCP Express is a lightweight version of CCP. You can use CCP Express to configure basic security features on the router's LAN and WAN interfaces. CCP Express is available on the router flash memory.