Map Themes in 3.7 and large WMS'

I have struggled with several ways to try and bring in a massive WMS into Geocortex 3.7 but have finally admitted defeat. Like Peter Timmers, we use the same WMS, which has hundreds of layers in it. 

We have several issues with this WMS that are possibly due to it's enormity. But if we could exclude layers in the xml without it crashing our sites, it could be more manageable. We found last week when they added new layers to the WMS that it completely shut our interactive maps down that include this WMS. Generally, in 3.5 to get around how slow it can make editing the site we got around this by only importing this layer at the Production stage from another site using the Import Service button.

With the Map themes in 3.7 I find that when in the Map Theme Menu I could not create themes with the BOM WMS included in the site (even if this was the only layer in the site). It would come up with a "500 - Internal Server Error" when I clicked on the Apply Details button. To get around this I created a separate site and edited the xml to include the various layers in themes that I wanted but when I tried to use the Import Service button to bring it into my main map it would let me add it but when I again clicked on the Apply Details button, the result was the "500 - Internal Server Error". 

Any suggestions or fixes?

Cheers

Bronwyn Kelly