Install-Uninstall .msi

Question

I have Visual Studio 2005 and Outlook 2007. My add-ins has install.msi file. When I need to uninstall it, I open 'Add or remove Programm' and choose my add-ins. Now I want to run install.msi file for uninstall my add-ins. If I run install.msi file, when  add-ins already installed in my mashine, I get message about error. If I change property 'ProductCode', I install other version add-ins.During the installation other version I can to check availability old version, but if I run 'MsiExec.exe /I{97257926-3443-4DB5-93CF-2B3ADAD581CC}', I get error'Another installation is in progress. To complete this process before the new installation.'.  How do I solve this problem? Do I need to convert install.msi file?