A few ideas:
1. You could try re-installing SM. After you uninstall SM, try renaming the Clam folder. My Clam folder is located in C:\Program Files (x86)\SmarterTools\SmarterMail\Service\Clam. This will give Clam a fresh start.
2. You may need the x64 and x86 version of Visual C++ Redistributable. You can confirm with SmarterTools.
3. Open ticket with SmarterTools.
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