"Unable to sacrifice Ollenbock Escort to grant invulnerability and +1/+1 counter"
That's now how the card works: it does not grant a +1/+1 counter. You can only sacrifice it to grant indestructible to a creature which *already* has a +1/+1 counter. If you don't have any such creature, you should not be able to sacrifice Ollenbock Escort.
"Unable to sacrifice Ollenbock Escort to grant invulnerability and +1/+1 counter"
That's now how the card works: it does not grant a +1/+1 counter. You can only sacrifice it to grant indestructible to a creature which *already* has a +1/+1 counter. If you don't have any such creature, you should not be able to sacrifice Ollenbock Escort.