This message means your document is too big to be scanned in one go. The maximum Viper can check in one scan is 89,000 characters (with spaces included). This helps to maintain the high-speed performance of Viper for all users. You can still scan your work, but you will need to split it into two smaller documents.
If you are planning to scan your dissertation, we recommend that you scan it chapter-by-chapter, as it will be more manageable and the results easier to understand.