I upgraded our exchange version to match the customers ( 18.104.22.16832 ) and following a restart of the server I am also now not able to delete signatures, I was able to in the previous release that i had installed 5.0.1 3982
1. Confirm that version of IIS component is "22.214.171.124"
2. Navigate to the folder on your IIS server : C:\inetpub\wwwroot\MailSignature\Views\SigBlocks
3. Rename the old index.cshtml to index.old
4. Replace with attached file