I've been using Spybot for a long time and it usually has no trouble with immunization.
Today I ran the immunization and it said Immunization is not complete, there are 15655 items still unprotected.
I'm running Spybot 2.7.65.0 with administrator privileges in Windows 7.
The only other anti-virus / anti-malware I'm running is MSE.
There are a couple things listed here that you can try:
https://www.safer-networking.org/faq/when-i-run-immunization-it-says-items-are-still-unprotected-how-do-i-fix-this/
You are already running Spybot as administrator, so that is already covered, but you could try temporarily disabling your other security program, as well as closing any browsers or programs that might be open during immunization.
MSE is Microsoft Security Essentials? Here are some instructions on how to temporarily disable real-time protection. Hopefully, the instructions still work with the newer versions of MSE, as I believe the instructions I found might be a bit older:
https://smallbusiness.chron.com/disable-microsoft-security-essentials-temporarily-72248.html
You might wish to temporarily log off the internet while having MSE real-time protection off, if that is applicable/possible for you. Please go back in and re-enable real-time protection on MSE (https://smallbusiness.chron.com/turn-realtime-protection-microsoft-security-essentials-51366.html) after you are done applying immunization, and please let me know how it went. :)