trendmicro office scan client update is not working anymore

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This morning, our trendmicro officescan server broke down and since
then, some of the clients are not able anymore to do the download of
the virus patterns.

After some research, I found out that the problem seems to come from
the IIS-download directory(web sites\officescan\officescan\download),
where the trendmicro publishes its downloads for the clients
(corresponds to the URL: "http://<trendsus-server>:8080/OfficeScan
/download/"). It seems that the client do not have anymore the rights
to download from there. If I understood well, trendmicro is using an
account IUSR_<servername> to download the updates, since this account
has anonymous access?

What I did is to give permissions for the group "EVERYBODY" and "DOMAIN
COMPUTERS" to the folder, thus all computers that are member of the
domain can now download the updates again, but all the computers that
are in a workgroup can still not perform updates.

What can be the reason for this?
Any idea for a solution?

Thanx in advance
Best regards

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