If this guide helped you, share it with fellow iOS enthusiasts. And always, always save your SHSH blobs early.
Apple only signs the latest version of iOS for public release. Once a new version comes out, Apple "closes the window" on older versions, meaning they stop sending SHSH blobs for them.
By methodically working through the solutions in this guide—from DNS changes to DFU mode and local SHSH flashing—you will likely resolve the error and get back to managing your iDevice with confidence. Remember: patience and the right troubleshooting sequence are your best tools.