Please check if you are following the below process to upgrade.
If you are on a version 3.x which is lower than 3.9.x, you first need to upgrade to 3.9.x. Please refer to this confluence page for the details.
If you are already on a version higher than 3.9.x and now trying to upgrade to version 6.x. First you need to upgrade to 6.10. This is because there are breaking changes in this version with respect to database structure etc.
Please refer to this confluence page for the complete details.
If you are following the process correctly but still encountering the issue, you may share the complete error message and version information.
Please check if you are following the below process to upgrade.
If you are already on a version higher than 3.9.x and now trying to upgrade to version 6.x. First you need to upgrade to 6.10. This is because there are breaking changes in this version with respect to database structure etc. Please refer to this confluence page for the complete details.
If you are following the process correctly but still encountering the issue, you may share the complete error message and version information.