Do you mean you have put tape that was recorded in an old Sony into a Canon HV20 that is connected to a Mac that is running iMovie to try to upload the old video to your Mac?
If so, you may not be able to make that work. At least some tape camcorders cannot play tapes that were recorded in a different device, especially a device from a different manufacturer. (I have kept my old Sony DCR-TRV17 to play back tapes recorded in it because they do not play reliably in my Sony DCR-TRV70.)
Use your old Sony for the upload. If you don't have the Sony but REALLY need the video, buy a used Sony of the model you used to record the tapes.
One other possibility is that old tapes degrade over time or might have been damaged in storage. If you are not certain that the old Sony-recorded tape is still good, you might want to try to rent or borrow a Sony to see if the tape will work before you buy a used discontinued Sony camcorder.
mehaul11 wrote: ... The tapes ... play back normally in the camera....
If you mean your Sony camera, the easiest solution I can offer is to use your old Sony for the import.
mehaul11 wrote: ... The tapes are not HD, do they have to be converted ... to be uploaded?
No. In fact, depending on which Mac OS, iMovie version, camcorder, and recorded formats you are using, having mixed formats on one tape can cause problems:
Depending on which Mac OS and iMovie version you are using, web-based tutorials are available in addition to your Mac's iMovie > Help menu command. Search Help for "import video" instead of "upload".
This Apple - Support - Search should give you a start with web-based help on the subject.