“…outlook.ost could not be accessed”

We have a user who, when he tries to delete or move any emails from his inbox the following message appears:

The file C:\Documents and Settings\username\local settings\application data\Microsoft\outlook\outlook.ost could not be accessed.

I’m not really the “IT guy” as such but things like this tend to come my way as I have a bit of ‘enthusiasts’ knowledge and our actual IT support is in another country, so any and all suggestions welcome.

I Googled the above message but it returns hardly any exact matches.

Cheers