I have users who are trying to passworld protect in this case a Excel spreadsheet on a Windows XP Pro box using office 2010 , when they try to password protect they get an error "Excel is unabe to encrypt your file, please contact your system administrator to resolve this problem."
this is on a local machine and not shared on the network.
I understand this is a known issue between win XP Pro and office 2010 and known fixed other then saving it to office 2003 format