Make sure you are using the correct version of Simba, .990/.991 iirc. Also, make sure you downloaded the newest plugins from Ben's thread, and placed them in your plugins folder. As for direct which java to use, I believe uninstalling 7 and googling java 6u33 to download that version might work? But if you have both a 7 and 6 downloaded, I swear there's a guide somewhere on the forums; I'll shorthand a way to switch, and look for the full version (I think posted by Brandon)
1. Find java in your control panel / press the window's key and search 'java' (might show as 'java (32-bit)' - side note: java 32 bit + simba 32 bit = stable/compatible

2. There should be several tabs in the Java Control Panel (window) that pops up. Out of your available options (I believe General/Update/Java/Security/Advanced), choose the Java tab: then the 'view' button.

3. Deselect the 7th version for java (no checkmark in the 'enable' box) and press the OK button (as long as your Java 6 update 33 is still checked…)

I think this is the correct procedure… I'll edit the post accordingly in the next few minutes
Edit : I think I was thinking of
this, but I also noticed
this (fully uninstalling java 7 from rs).
If you read through this whole post, I think it should take care of the java side needed for smart.. I'm also unsure if the system tab (when in the java control panel) needs to somehow remove the java 7 too. Just trying to help / hope this helps - if there's mistakes / this is wrong somebody say something >.<