I had the same issue but with a ladder char. The root cause is not known but the hypothesis is that I used a golem relic on an armor. After made some changes the char no longer had strength to wear the armor. The work around was to ask ladder admin to delete the iron golem.
It happened to me twice. The first time was that I respec'ed my char. Second time was I gave some charms to another char.
Not sure how you handle this in SP.