UrBackup cannot create shadow copies on TrueCrypt/VeraCrypt container volumes. It therefore cannot backup open files and you may see warnings if files change during backup. This is a TrueCrypt/VeraCrypt limitation. From the former TrueCrypt FAQ page:

The Windows Volume Shadow Copy Service is currently supported only for partitions within the key scope of active system encryption (e.g. a system partition encrypted by TrueCrypt, or a non-system partition located on a system drive encrypted by TrueCrypt, mounted when the encrypted operating system is running). Note: For other types of volumes, the Volume Shadow Copy Service is not supported because the documentation for the necessary API is not available.