Instalation problem from 1.5.x to 3.0.3.2

Hello All.
I try to upgrade my opencart from 1.5. When I hit "Continue" on the Upgrade page, after a while, I get the message: "Internal Server Error Internal Server Error Error: A theme has not been assigned to this store!"
I attached the screenshot from the website.
Please help me resolve this issue.

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Best regards
DK

For upgrade issues, please create a new service request in the Commercial Support section of the forum, or contact me directly, to get this issue investigated as a custom job.

You were not using the default theme on OpenCart 1.5 and it didn't match with the structure of Opencart version 3.0. To resolve it, before the Opencart upgrade process, access to admin->extension->extension-> theme. Choose the default theme and enable it or you can also remove your current theme, then save it in admin->system->settings, and do not forget to clear cache.

If it works, please let me know your opinion

ashleybr217 wrote: ↑

Fri May 01, 2020 4:25 pm

You were not using the default theme on OpenCart 1.5 and it didn't match with the structure of Opencart version 3.0. To resolve it, before the Opencart upgrade process, access to admin->extension->extension-> theme. Choose the default theme and enable it or you can also remove your current theme, then save it in admin->system->settings, and do not forget to clear cache.

If it works, please let me know your opinion

Not enough. Manual database patching also needs to be done to apply such an upgrade.

I revert to my 1.5.x version and confirm that I was using default theme. So I think it is something more. In the instruction attached to the new version the upgrade looks so easy

dkaczmarek wrote: ↑

Fri May 01, 2020 9:29 pm

I revert to my 1.5.x version and confirm that I was using default theme. So I think it is something more. In the instruction attached to the new version the upgrade looks so easy

Depending on the store's condition and the mount of total database values it may contain, the procedure may become more complicated when store owners don't know how to deal with them. Which is why, it is highly recommended to seek for professional assistance from the Commercial Support section of the forum, or to contact a reliable developer, to complete such upgrades without impacting the stores.