While installing mythtv 0.20 using ubuntu 6.10 I made an error in the configuration. I chose us-bcast instead of us-cable. This error caused the program scheduler to create entries in the mysql database that were two channels off starting at channel 15. As example, channel 44, the Sci-Fi channel was actually on channel 46. If you selected 44 from the program scheduler you got whatever was playing on channel 42.
After trying to correct this by changing the configuration and downloading the program schedule from datadirect serveral times I decided to try deleting the mythconverg database using the directions in the mythtv how-to relating to deleting the mysql mythconverg database.
After the deletion and recreation of the database and the correct selection of configuration options the program channels now lined up correctly with the program guide information.
In a previous troubleshooting guide the only mention of channels being offset referred to the tuner type being incorrectly selected and causing this error. Since the tuner on my PVR-150 was correctly identified by ubuntu's ivtv drivers I did not see that suggestion as being valid.
I hope this message will help someone else out that might make the same mistake in the future.