Further version of Microsoft.Navision.Mail.dll cannot be registered again?

FragenFrager

Hello,
currently I have the following problem: I have implemented a hotfix that concerns the table 409, the form 409 and the CU 400. Additionally, I have replaced the Microsoft.Navision.Mail.dll by a newer version and registered this new version with regasm (regsvr32 doesn't work completely).
It has unfortunately been found that the hotfix has not brought the desired result, so I wanted to change it back. So I have exchanged the Navision objects against old objects, just back secured the old Microsoft.Navision.Mail.dll again and registered. The CU400 will compile without problems. If I now however call it, I get the following error:
"Could not create an instance of the OLE Control or Automation Server GUID = {68EAA7B-9523-3511-AF5F-F2381D2C6F04} 1.0 {F9DAE2A4-D2F8-37C3-86D5-E4FFE166D860}: 'Microsoft Navision Mail'.SmtpMessage. Check that the OLE Control or Automation Server has been correctly installed and registered.
I also deregistered the .dll and registered back again, same result :-(.
Has anyone here an idea what I could try next?

With kind regards
FF