When you receive this error message:
Could not complete the operation. One or more parameter values are not valid.
while addressing or sending an email message, meeting request, or assigning a task, or saving a new contact, your auto-complete list may be corrupt. Some users also report getting this error when they save an appointment or task.
The solution: clear the auto-complete list cache.
Outlook 2010: Clear Names from the Auto-Complete List
To remove single addresses, select the name using the arrow keys then press Delete. In Outlook 2010, you can also click the x beside the name to delete it or use the Backspace key.
You can also close Outlook and use the /cleanautocompletecache startup switch. To use, press Windows key + R to open the run command then paste
in the Open field and press OK.
Outlook 2007 and Outlook 2003
To remove single addresses from the list in Outlook 2007 or Outlook 2003, select the name using the arrow keys then press Delete.
In Outlook 2007 and Outlook 2003, you can remove all of the addresses from the autocomplete cache, either by deleting the NK2 file (at %USERPROFILE%\Application Data\Microsoft\Outlook ) or by opening Tools, Options, Email Options, Advanced Email Options and deselecting the option to suggest names near the bottom of the dialog.
For a list of utilities you can use to edit the auto-complete cache, see Understanding Outlook’s Auto-Complete Cache (*.NK2)