I had also experienced this on an upgrade in my lab a few days ago and after some persistence was able to resolve it only as follows.  I chose to uninstall everything (from within vSphere Client and then Add/Remove Programs) and start from scratch.  However, as you'll read and as you also experienced, curiously even that is not enough.  The key is to rerun the original installer for any that fail with the error message above.  Only then does the specific feature get removed completely and properly let you install the new.  I am doing this from memory and arguably is probably more than necessary having identified the specific issue, but I'll share what worked for me.    1) Uninstall plug-ins from within vSphere Client a) From the vSphere Client Home view, select the "VSI" button b) First note the version of the EMC VSI features currently running c) Right-click on each feature and select "Uninstall"   2) From Add/Remove, uninstall the VSI framework and supporting components: a) Uninstall "EMC Virtual Storage Integrator (VSI) for VMware" b) Uninstall "EMC Solutions Enabler" (if running locally and dedicated to the VSI Storage Viewer plug-in) c) Uninstall "EMC Unified Storage Access Control for VMware" (if installed)   This next step is the key (and may be enough instead of doing a complete uninstall of everything as I did during my troubleshooting having now identified the specific issue):  3) For the specific plugin that returned the error message when trying to upgrade, rerun the installer of the version that was running originally. a) Download the original versions of VSI features from PowerLink as noted in step #1 above b) Rerun original installer only for any of the new features that return the error above c) You will be prompted with an option to "Uninstall/Remove" which you'll want to perform.  NOTE: For me, even though I had older versions of all 3 VSI features running (USM, SV, and PM), I only needed to concern myself with USM (tried to upgrade from v5.0.0.86 -> v.5.1); however, it may be possible that the other features if upgrading will experience the same behavior and the remedy should be the same.   4) Install the latest VSI features Due to another bug which I experienced but turned out is actually documented, you'll want to first install any feature that includes the v5.1 framework first (as of this writing):  Unified Storage Management or Storage Viewer (Path Management feature is still at v5.0 and should not be installed first if you choose to uninstall everything).  emc285999: "After an upgrade to version 5.1 the VSI Storage Viewer returns error "Unable to load DLL ‘SEWrapper.dll’: The specified module could not be found. (Exception from HRESULT: 0x8007007E)"  Alternatively, as noted in the KB article you could install the Microsoft Visual C++ 2010 Redistributable Package (x86) if you get the error as I did when I chose to reinstall the Path Management feature first.   5) Verify that the VSI plug-in is enabled a) Within the vSphere Client, from the "Plug-ins -> Manage Plug-ins" menu bar, verify "EMC Virtual Storage Integrator (VSI) for VMware" is enabled b) If not, right-click and select "Enable"   6) Rediscover the arrays a) From the "Home" view, select the VSI plug-in b) For both the Storage Viewer (test the local Solutions Enabler connection also) and the Unified Storage Management feature, rediscover the arrays
I am having issues getting the latest VSI plugins to install. I had the 5.0 version working fine and I tried to both upgrade and clean install of the latest ones and they are failing to install every time. I get the following errors:  Setup failed to configure the server. Refer to the server error logs and setup error logs for more information.  and after hitting ok I get:  The wizard was interrupted before EMC VSI for VMware vSphere: Unified Storage Management could be completely j... Your system has not been modified. To complete installation at ; another time, please run setup again.  When I check the Vsphere client they are showing the plugin installed but it can't be enabled and it also shows up in Add/Remove Programs. 
Error Trying to install VSI 5.1