Tag tagname does not contain a valid integer: tagvalue
The value specified for the tag was not a valid integer.
For example, the config.txt file for a traincar included the tag line:
which created the error message:
VE191: Tag 'custom-attachments' does not contain a valid integer: a.load0
The correction is to change the tag value in config.txt so that it is a valid integer number. However, in this particular case the validation for the tag is incorrect, and the tag is deprecated, so the fix is to remove the line from the config.txt file (gameplay should be unaffected in any version as far back as TS2009).
A valid integer number consists of an optional minus sign and one or more digits.