Internal error when opening catalog

Question

I used Lightroom on occassions and created a catalog for a folder with 4000: files and subfolders (named foo in this story)
It worked.
Today I openend Lightroom
Immediatly after opening choose the folder foo and synchronized
Result an error
"An internal error occured: Database ....\..."
The file lightroom4_catalog.lrcat still exists on the right location.

Answer 1

Ah, the problem is that you're trying to call myRootKeyword:getName() before exiting the catalog:withWriteAccessDo().  The doc for catalog:createKeyword() says:
Must be called from within one of the with__WriteAccessDo gates. The new keyword is not available for access until that function returns.
If instead, you restructure your code like this:
local myRootKeyword
catalog:withWriteAccessDo("setKeywords", function () 
    myRootKeyword = catalog:createKeyword( 'People', {}, true, nil, true )
    end)
It works just fine.
By the way, your comment "Crashes after this line" was incorrect.  I suggest you use the Debugging Toolkit, which will make it much quicker to identify your bugs. It will take some time to hook it up the first time, but it will pay off pretty quickly.