This is a Cisco Network Assistant (CNA) error when you want to telnet any Cisco Devices from within CNA.
Solution to remove this error is related to Windows 7 or Windows Vista.
First of all you need to Add TELNET program from Control Panel, which by Default is not added in fresh installation of Windows 7.,
Click Start > Control Panel > Uninstall a Program > Turn Windows Features On and OFF > Scroll to TELNET and Select it > Press OK
After Adding Telnet Program into the Windows 7 you need to Copy Telent.exe from C:\Windows\System32 folder and paste it to C:\Windows\SysWOW64\
Now you should not get the same error.