"String missing" error on the signature capture window
The "String Missing" error occurs when the signature capture component has a problem loading localized strings.
The strings should be in 'MUI' files in language specific sub-folders of \Program Files\Common Files\WacomGSS (or \Program Files (x86)\Common Files\WacomGSS on Win64).
An uninstall/reinstall of the product (SignPro and/or Signature SDK) should fix the problem.
To be on the safe side, after uninstalling the product(s), check that the "...\Common Files\WacomGSS" folder and all subfolders have been removed.