SUM upgrade error in Execution phase at step: " MAIN_SWITCH/SUBMOD_SWITCH_KERNEL/ENVFILES!"

Hi experts,

I am trying the upgrade our SAP Solution manager 7.1 SP11 to SP13 using Software Update Manager [SUM] SP13 on windows system.

I got the following error in execution phase. Please advice

Severe error(s) occurred in phase
MAIN_SWITCH/SUBMOD_SWITCH_KERNEL/ENVFILES

Last error code set: Cannot query 'PATH' in registry key
HKEY_CURRENT_USER 'Environment': The system cannot find the file
specified. <br/>

thanks,

Raja.