The forward slash in the case name prevents the deletion of the case. An ampersand, percent or plus sign also causes the same issue.
Note : The plus sign does not show any error. The percent sign shows a red zero. Ampersand shows the Invalid case backup error.
Workaround
1. Navigate to the Case Backup location and locate the archive folder
2. The case archive folder name will be 0.6.31.346939725-NameOfCaseWith@u002FForwardSlash where the forward slash has been replaced by @u002F
3. Rename the folder to remove the @u002F eg. "0.6.31.346939725-NameOfCaseWith@u002FForwardSlash" becomes "0.6.31.346939725-NameOfCaseWithForwardSlash"
4. Inside this folder are the backup and archive folders
5. Inside the archive folder is caseBackup.properties file
6. Open caseBackup.properties file in Notepad, locate the line"caseName=NameOfCaseWith/ForwardSlash" and remove the slashes to become "caseName=NameOfCaseWithForwardSlash"
7. If there are more than one archive or backup folders, repeat the editing of caseBackup.properties file in each folder
8. Once completed, return to All Cases > All Processing > Archives and delete the archive.
The Ampersand (&), Percent (%) and the Plus (+) Signs, are not substituted in the folder name and simply need to be removed from the folder name and also from the caseName in the caseBackup.properties file.