Iis – User account can’t connect to IIS6 FTP site

I set up a new virtual directory in IIS under the Default FTP Site. I already have other virtual directories, and I'm able to access them with my user account, which is a domain admin. I created an account named FTPuser, gave it full permissions to the virtual directory, but I can't open the site. When I log in, I get a Success Audit event in Event Viewer, so my account is being authenticated. But the site doesn't appear, I just get the login box again.

I ran Process Monitor and saw different behavior between the two login scenarios. When I login to the same FTP site with my admin account, I get a SUCCESS result in Procmon when trying to access the folder that is specified as the home directory for my Default Web Site. But I get an ACCESS DENIED message when trying to connect as the FTPuser. Above that in the log, it also shows a NO SUCH DEVICE error trying to connect to the IPC$ share on that drive (the one containing the home directory).

When I look at the permissions, both accounts seem to have Full Control on the relevant directories. Can anyone point me in the right direction as to what is going on here?

Thanks.