Symantec Mail Security for MSExchange - SMTP Violating Policy Settings

Hello,

I keep getting the following alerts:

- Provider [Name]   Symantec Mail Security for Microsoft Exchange 

- EventID 303  [ Qualifiers]  32791   

- Level 3   

- Task 23   

- Keywords 0x80000000000000 

- TimeCreated   [ SystemTime]  2012-12-31T15:47:27.000Z
 
- EventRecordID 63669077

- Channel Application 

- Computer xxx.xxxx.xxx

- Security

- EventData

   attachment
   G234-G236.zip
   message with subject "G234-G236 Client Reports", located in SMTP
   Scan: Auto-Protect Rule: Encrypted File Rule 
   The attachment "G234-G236.zip" was Logged Only for the following reason(s): Scan Engine error in decrypting a file in a compressed file

I have this error comming up a few times a day, and generally from different people on different machines from assorted email address'.  There doesn't appear to be any "error" on the user end, but I'd like to know why I'm getting this and if I need to make any changes.  Any assistance is appreciated.