This is definitely an access problem. I also got this error when trying to write data to a Datsocket server on another machine. It turns out I needed to give CREATE priveleges to my machine (or everyhost) using the Datasocket Server Manager.
To fix access problems when writing to Excel, here are some reccomendations:
-Make sure excel isn't already open. Sometimes it might be open, but hidden. Check the NT Task list to make sure excel.exe isn't running.
-Check dcomcnfg priviliges and security. Type dcomcnfg at the command prompt and check the secutiry setting for Excel.
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