does it matter if I render the preview files in premi�re or not. Does this effect Encore.
It should not matter. But they must be Bluray legal.
I assume by "render" you mean export; is that true? You might also mean "render" and you are dynamic linking.
I assume by "segment," you mean "Premiere sequence"; is that true? You might also mean a segment of a PR sequence (i.e. using only the work area rather than the whole sequence).
I'm having trouble understanding which files you are actually working with.
We need to know whether Encore is working. If it is, it should import an m4v even if it is not legal and Encore is going to re-transcode it. My suggestion to use one of the old files that worked in the past was designed to test that.
It is important to use a new Encore project with a new name.
Another test is to export a short piece from Premiere, use the H.264-Bluray preset and change nothing, create a new Encore project, and import as timeline that m4v.