@Siddhu Yes that is an rc3 introduced bug by the looks of it. I will get a version out tomorrow to fix that. It is caused by having N1MM spectrum turned on.

You can edit the database.xml file to get around it for now, located here : C:\Users\<user>\AppData\Roaming\OpenHPSDR\Thetis-x64

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I just patched with release 21k9rc3 and performed a database update as well. I'm getting this error while opening Thetis