Help me, please. Why does this error occur and how to fix it?

[thisCatIsPolite]

Here is my project structure:
I don't understand why this error always occurs. Here is my project's structure:

 

[PetteriM1]

Does the plugin still work? I sometimes get class not found exceptions with devtools even evrything works. You can also try to delete src_compile folder to see if that helps.

 

[thisCatIsPolite]

Does the plugin still work? I sometimes get class not found exceptions with devtools even evrything works. You can also try to delete src_compile folder to see if that helps.

No, plugin doesn't work. Ok, I'll try your advice

 

[thisCatIsPolite]

Does the plugin still work? I sometimes get class not found exceptions with devtools even evrything works. You can also try to delete src_compile folder to see if that helps.

No, I've deleted this folder and plugin is still broken