I'm running Windows 10, Office 365/Excel. The add-in Solver doesn't work though Goal Seek works fine for the solution to the same set of data. I tried uninstalling/reinstalling Solver without benefit. Also ran the Quick Repair app from Control Panel without benefit. Any suggestions?
Having just struggled with this problem here is what worked. I just moved from Office2016 to Office365 Even though I had originally been running a 64 bit install on Office 2016 and Windows 10 is a 64 bit version, with Office365 I needed to install the 32 bit version in order to resolve the problem. The issue appears to be with the Solver32.dll file.