Few things to try, Ensure the Framework and all it’s headers are imported into your project properly.
Also in your Build Settings set YES to Always search user paths, and make sure your User header paths are pointing to the Framework.
Finally, Build->Clean and Restart Xcode.
Hope this helps !
UPDATE: According to SDWebImage’s installation, it’s required you make a modification to Header Search Path and not User header paths, As seen below.
Have you done this as well? I suggest slowly, re-doing all the installation steps from the beginning.