The permissions are cached with their own cache id, so you might need to flush the cache after changing permissions.
Speaking of cache, if you are on 1.9.2.0 there is a cache bug with static blocks: Magento 1.9.2.0 static block display issues It's unlikely, but this might be related your problem if you have a multistore setup where the logo is not configured for every store.
Other than that, the code you show is correct, so it could also just be a misspelling in the variable permissions. Pay attention to leading and trailing whitespace, which is not trimmed automatically.