The error appears when there are insufficient user access rights on the specified drive, as shown by this sample snippet of the SMEX_RIFRemoteInstallAgent.log:

2011/08/16 17:36:13 GMT-8:00 [04672:04808] [          RIFRemoteInstallAgent.cpp( 1094)]  DEBUG     Load Resource DLL: RIFResCommonDlg.dll  2011/08/16 17:36:13 GMT-8:00 [04672:04808] [                rInstConnection.cpp(  270)]  DEBUG ==> rInstConnectionRegistryImpl::SerializeDataFromMaster  2011/08/16 17:36:13 GMT-8:00 [04672:04808] [                rInstConnection.cpp(  276)]  DEBUG     Filename is: \\?\UNC\target-exserver\E$\smextemp\RIFCONNECTIONFILE  ..  .  2011/08/16 17:36:13 GMT-8:00 [04672:03408] [                     rUtilLogon.cpp(   24)]  DEBUG     Logon as ACCRETIVESOLUTI\sysadmin, LogonType= LOGON32_LOGON_BATCH, LogonProvider= LOGON32_PROVIDER_DEFAULT  ..  .  2011/08/16 17:39:28 GMT-8:00 [05652:06640] [                 rUtilMsiHelper.cpp(  269)]  DEBUG     Progress: Error 1923.Service ScanMail for Microsoft Exchange Master Service (ScanMail_Master) could not be installed.  Verify that you have sufficient privileges to install system services.  

When the drive letter is changed to another shared drive, make sure that it has the Read/Write/Execute security permissions for both local Admin and ExOrgAdmin users to avoid installation problems. Otherwise, just leave the default shared drive "C$", which is already configured with the required access rights for local/domain administrator accounts.

Below are the installation log/s directories, for further reference.

Remote Server:

• {System temp}\SMEX_RIFRemoteInstallAgent.log
• {SMEX Installed folder}\Debug\All log files
• {SMEX Installed folder}\SMEX_DatabaseCreation.log
• {System temp}\instDetectClusterType.log

Local Server:

• {Logon user temp folder}\setup.log