How to tell my possible employer about a technical showstopper in performing a task

I've been contacted as a freelancer about a project. It's not my field of knowledge exactly, as it's in a different language and all that, but we agreed it should be trivial to learn it and related technology in a timely manner. When I felt I know enough I was given a test project to show my skills. The tasks are quite simple and aren't the obstacle to the job. The bummer is that one of dependencies just doesn't work with a cryptic error message. The search on the Internet I've been conducting for the past week doesn't get me anywhere, and I'm getting progressively anxious and frustrated, since no proposed solution is applicable or working for me. I've tried asking in relevant IRC channels and in the official mailing list, but have gotten no responses so far.

While I was given "as much as you need" time to complete the tasks, I've not really done anything meaningful due to this since the error prevents the project from running at all.

How can I explain my situation the best to the employer? I feel I need to let them know I've not gotten anywhere, since just waiting for the problem to go away won't work, and probably they could have already encountered the exact error and could guide me in fixing it or at least decide to let me go right away, just so I wouldn't get worked over it too hard.

Yes, talk to your manager/contact about this.

Lead with the positive about what you have achieved and learnt so far and show that you understand the platform enough to work on this.

And then lead into your problem by describing your reasoning for going down that route. Describe the issue and then ask for how you should continue this.

Admit to yourself that this might not be the right approach and that looking at this from another direction might be more appropriate. There's been plenty of times where I've come against a brick wall only to find out that my approach has been all wrong. This happens, we all tear down walls or find another way of doing something. We're all learning.

Be honest about it, and ensure that the experience is positive and forward looking rather than blocking.