I think the problem isn’t related to the opining of the S2 image file, but You need to update your SNAP, (Which version do you use?) Remove the iCOR and Re-install it as I explained to you in the previous post,
Because the first show of this plugin should be this,
Then selecting any of iCOR, let’s say iCOR-S2 will give you this panel,
When you navigate to the source product, this panel directory should be appeared,
Select the MTDD…*xml file, the product will be opened, as the following,
