If there is a red '!' icon on your Box it means one or more of your files have failed to convert or be processed by the AI. This is most often due to the file(s) being unsupported for conversion or analysis within Smartbox. You can see the list of supported file types here.
This error indicator does not mean the rest of your files have failed to process, so do not delete the Box. If a file is not supported, the AI will simply move on to the next file rather than failing the entire process.
To identify the cause, locate the failed file and hover over the red 'X' icon to reveal the error message. If the filetype is supported but has failed to convert, you can try deleting it and re-uploading.