After disabling, try the SHSH request again.
You are using an old version of 3uTools that doesn't support the latest iOS protocols. 3utools error unable to request shsh hot
Ensure the firmware you are trying to flash is actually "Signed." In 3uTools, look for a green "Signed" status next to the firmware version. If it is "Unsigned," you cannot flash it without previously saved SHSH blobs. After disabling, try the SHSH request again
: Your version of 3uTools may be too old to communicate correctly with newer Apple server protocols. Network Issues 3utools error unable to request shsh hot