"unable to be" used with incorrect subject?

I see this phrase used a lot, and always thought it to be incorrect, but I see more and more people using it so I'd like to find out if I am wrong or not.

As an example the following sentences:

The samples were unable to be collected.

Sampling was unable to be performed.

It seems to me that the subject here are the samples or the sampling, therefore it is incorrect to use "unable to be" when they are describing an action that was to be done by someone else.

I would rather say one of the following

We were unable to perform the sampling.

We were unable to collect the samples.

The samples could not be collected.

The sampling could not be performed.

Do these last two have the same meaning?

Solution 1:

Passive voice has a great way of obscuring meaning...which is partly its point. It leaves ambiguous the actor or agent.

I did not do it. vs. It was not done.

So, considering the question, I believe most writers and speakers would consider these phrasings to be equivalent:

The samples { weren't / couldn't be / weren't able to be } collected.

Whether samples themselves have any influence on their ability to be collected, the condition of an object could affect its collectability.

The samples were so degraded, they were unable to be collected.

The samples were so degraded, they were incapable of being collected.

The samples were so degraded, I was unable to collect them.

The sentences really mean the same thing; the third just takes more responsibility.

I agree wholeheartedly with Mr. Ashworth's comment above, that it can't be established if one way is the only "right" phrase grammatically. You can argue whether it sounds wrong to give a quality of able-ness to a thing, but "unable to be collected" and "unable to sing opera" are not quite the same level of capability.