Symptom

Opening a Visum version file fails with an error message:
"Checksum error when unpacking ‘Matrices/Matrix<X>.bin’"
"Cannot read version file ..: Matrices/..bin is damaged"

Cause

Faulty storage media or network connections can compromise large binary streams, typically large matrices and assignment results have a higher probability to suffer from this. Before PTV Visum 2021 a change to just one bit changing the meaning of a single matrix value remained undiscovered. The occurrence of this error message is therefore not the result of a program error.
Since PTV Visum 2021 the ZIP format is used to store the contents of the version file, which also includes checksums for all parts of the version file.
The integrity of all parts of the version file can also be checked manually by opening the version file with 7-Zip and running a CRC check via “File -> CRC -> CRC32”.

Resolution

Use 7-Zip to open the version file and check the integrity of the matrix or table mentioned in the error message. You will not be able to recover a compromised matrix, but you can delete it from the archive and thus recover at least the version file. If the checksum error occurred in any assignment result (i.e. the error indicates a damaged file in the “AssignmentResults” subdirectory), all files in the folder “AssignmentResults” can be deleted from the version file to be able to open it in visum.

Disclaimer

Please always create a backup copy first before modifying any content of the version file with an external program like 7-Zip.
Also note that if the damaged file is neither a matrix file nor any of the assignment results, deleting that file may cause the Visum data model to be in an inconsistent state and cause errors loading the version file or even cause errors when working with the model at a later time point. In such a case, we would generally recommend to not work with that recovered version file directly, but to export any network data as text files like NET, DMD, etc… and read that into an intact backup copy of the version file or a new version file.