Error with exchangeserver.msi file when adding feature to Exchange 2007 on SBS2008

Today I am installing the Unified Messaging role on my SBS2008 Exchange 2007 install.    I am going to be implementing the excellent 3CX Phone software on our network for test (more on that later!).

During the installation of the Unified Messaging service I got prompted for the EXCHANGESERVER.MSI file because the SBS2008 installation gets rid of the files it temporarily creates during setup in C:Program FilesWindows Small Business ServerBinCMPNENTSEXCHSRVR80

Simple, I thought…   just point it to the CDDRIVE:CMPNENTSExchange12 directory and we should be good to go…   but alas, this is not the case.   I ended up with this error:

Installing product E:CMPNENTSExchange12exchangeserver.msi failed. Fatal error during installation. Error code is 1603. Last error reported by the MSI package is ‘An installation package for the product Microsoft Exchange Server cannot be found. Try the installation again using a valid copy of the installation package ‘EXCHANGESERVER.msi’

Very odd.

After some research and general screwing around with things, I copied the Exchange12 directory from the CD to the hard drive, and pointed to that instead…. sure enough, the installation continued on without issue!