SUMMARY

When MailEnable is installed or when manually attempting to register components of MailEnable, error code 0x80004005 is generated.

The description of the error is: DllRegisterServer failed on component install. This may occur when using regsvr32.exe or if registering components in COM+.

DETAIL

This error can occur if not logged into the server as an Administrator (or suitably priviledged account). This problem is not specifically a MailEnable issue as it applies to all COM/ActiveX DLLs.

When registering COM components, the installer needs to write in the Windows registry in portions that may be restricted.
Specifically, the HKEY_CLASSES_ROOT\TypeLib registry branch (and children) should have full control granted to Administrators.
 
If (for one reason or another), Administrators do not have access to this directory, grant access (and ideally determine why access
was removed). Granting permission to the branch can be done using the regedit32 utility (see Microsoft Knowledge Base for examples of using the utility if not familiar with Regedit). Before using the utility, backup your registry. 

Another alternative is using the RegMon utility from www.sysinternals.com to diagnose any other inappropriate registry permissions.

MORE INFORMATION

REFERENCES

Regmon: http://www.sysinternals.com