To fix this error in HandiTax "app failed to start because side-by-side configuration is incorrect"
Close the HandiTax year affected.
Navigate to the HSoft\Apps Folder
Rename the HtXX.exe.Config file (or for SQL: HtXXSql.exe.Config) to HtXX.exe.ConfigOLD
xx represents the year of HandiTax eg. HT22.exe.configOLD.
Re-open HandiTax. This will generate a new config file and the error should be resolved.