We can't know. You have not offered any info about your project, the type of sources for the missing layers, your computer and so on. the error is just a generic math error. If the layers are of a specific type it could simply indicate that some component required to handle the files has changed like e.g. a CoDec or a shared file handler for instance foir Illustrator. Similarly, if there are text layers, a font could have changed/ been replaced and gone "bad". There could also be cache issues with these layers. Who's to know? Just too many possibilities. You need to be more specific.