I'm using an AVCHD camcorder (Sony DCR-SR60). I created a project in Premier Elements 9.0.1 on the Mac with the preset "Harddisk, Flask Memory Camcorder - Widescreen 48 khz". Any exported video includes vertical lines due to improperly set field order.
After some research in the forums (thanks everybody for the helpful insight!) I know now that I should have used the preset "AVCHD LITE 720p30" instead. For new projects that solves the problem: no vertical lines and great video quality.
However, for the existing projects I tried to reverse the field dominance in the sceneline view (menu item "Clip - Video Options - Field Options - check Reverse Field Dominance"; needs to be done one clip at a time), which is supposed to also solve the problem based on several forum posts. When I tried it that solves the issue on Windows (version 9.0, have not tried 9.0.1), but it does not work on the Mac (Premiere Elements 9.0.1 on OSX 10.6.6 with the Quicktime MPEG-2 playback component installed). On the Mac the exported video still has the vertical lines in it.
Any help or ideas would be much appreciated.
OK, after trying out various alternatives I found an acceptable workaround, so I'm answering my own question. I ended up exporting from the Premiere Elements project (the one that used the wrong preset) to the Quicktime format. I then created a new Premiere Elements project that uses the AVCHD preset, imported the Quicktime movie into this project and exported to MPEG from there. That solved the issue with the vertical lines and I don't think there is a noticable quality loss due to the multiple conversions (first to Quicktime, then to MPEG). Interestingly enough the Quicktime movie has some shadows on fast moving scenes (I'm guessing that's related to the issue with the vertical lines), but that's all gone by the time the final MPEG is created.
So that works for the few existing projects I have and using the AVCHD preset solves the issue for new projects and does not require this workaround.