Network resource that is unavailable

I am trying to update and it says "The feature you are trying to use is on a network resource that is unavailable. Click OK to try again, or enter an alternate path to a folder containing the installation package 'AcroRead.msi' in the box below...After searching my PC the only one that contains 'AcroRead.msi' is the one that is in the Use source box. HELP!