Can anyone help me with this one!?

I uploaded a fresh install of Umbraco 6.1.6 to a shared server where I have multiple Umbraco installations. (not my server)

When I upload a couple of files, the application pool crashes, giving a 503 error. Very unsettling behavior. Never seen it before.. I cannot possibily delivery this to the client, as it doesn't work properly.

The last call that is made before crashing is mediauploader.ashx. In some way, its generating an error.

Does anyone know what I can do about this?

Martin