Sometimes when you are trying to export projects ton older versions of GCS900 e.g. v12.3 you will be presented with a host of errors stopping you from exporting the data. While the errors point to the issue being a host of reasons, the likely cause is that you did not install the correct GCS900 version components when installing TBC.
There is a point in the installation process where you can select optional items for install - in that section there is a section for field data like GCS900 and in there you will find a checkbox that is OFF by default that you need to check to install the components that support the older versions of GCS900.
I think the above option went back as far as 12.3 in the 2023.11 version of TBC - in the upcoming release it appears that they are no longer supporting the older versions of GCS900 - so you may want to keep an older version of TBC around to support the older versions of GCS900 going forwards.
If you install those then you will likely find that you can export designs to the older versions of GCS900 and that all the errors and messages that you were receiving earlier go away.
Alan