Collada exporter + Decimate -> WebGL GL_INVALID_OPERATION

Hello, it’s my first post here.

I have a Collada model that I’m rendering in the browser with WebGL (using the Three.js Collada loader).

This works fine, except my model is about 15MB so I need to reduce it down. I’m a real newbie, but I read up that the Decimate modifier should do this. Sure enough, it reduces the filesize. However, if I decimate and re-export to Collada, it no longer renders in the browser. Instead, I get:

‘GL_INVALID_OPERATION: glDrawXXX attempt to access out of range vertices’.

Apologies if I should really be posting this in a WebGL forum instead (if so, I’ll go find one), but I thought maybe this was a good place to ask for advice?

Thanks very much,