I tried to install EPiServer.Forms on a EPiServer Alloy site upgraded to Episerver 9.
I recieved this error on two different sites after installing EPiServer.Forms from nuget.
Unable to find a module by assembly 'EPiServer.Forms, Version=188.8.131.5200, Culture=neutral, PublicKeyToken=null'Parameter name: moduleAssembly
Did you copy the appData folder? Sounds like it found the dll in bin but can't locate the module files?