Not familiar with an issue where the render doesn't work and export does (I've always had export fail, too), but when I've had those issues with rendering/exporting, it's always been one of two problems: a) I've got a "black hole" in my video where there's a couple frames without any video in one of the tracks, or b) I've got a still image that's too big for Premiere to process.
Honestly, though, unless you've checked the box for the export to "Use Render Files" in it's encoding, there's no need for you to render before you encode. I never do, and I have beautiful results. The only time I ever render is if I need to have a smooth playback of a complex timeline involving several layers of RED material and I need to have smooth playback at 100% for client approval before the encode. But even then, I never let the encoder use those render preivew files...
My understanding is that it's easy for those files to get corrupted, so you can end up with unsatisfactory results in your export by using them.
My understanding is that it's easy for those files to get corrupted, so you can end up with unsatisfactory results in your export by using them
Not only that, but preview renders are not always the best format for your export, since they are based on your sequence settings. Your export settings may differ. For instance when using MRQ or using a combination of different framerates in your source material, say 25 and 29.97 FPS. Generally it is ill-advised to use preview renders on the final export unless the source material, sequence settings and export settings are identical.