Umm, ok. If you look at that error it tells you flat out... how do you expect to call on a CLSID (registry object) that you don't want to install in the server?

Inorder to create the XLS file (which is an object) you will need to object registered in the system registry in order for InteropServices to invoke methods from it.

Sorry dude, but you will have to install Excel at the minimum to have this work, at least to my knowledge anyway.

Reading from an excel file without excel installed is on thing, but creating one through method calls to it...is another.