"The blocks area did not load properly...". Backpack is unaccessible

I've been experimenting with code to handle ASCII character messages imported via a serial port. When I now attempt to load the project I get the message "The blocks area did not load properly. Changes to the blocks for screen 5297754328137728_Screen1 will not be saved.". Unfortunately, I had added the code to the Backpack, which is no longer accessible, though the Backpack icon suggests it does hold blocks.
Is there any way I can recover the project and the content of the Backpack?
I was very surprised that the Backpack became inaccessible as well as the project.
This is one of my first project with App Inventor, which look like a great tool but with some frustrations, such as this method of handling what I presume are my errors.
Grateful for any help you can suggest.

Hi TopCat

This is a known issue that we hope to have fixed in the next release - the ASCII message contained non-printing characters. So not your error at all.

If you can save the Project and Export it to your PC (which is good practice to have backups at each pertinent moment in your project development) , post it here and I will see if I can clean it up for you.

Here is the aia file:
Test250Reader20210303.aia (207.4 KB)
Many thanks for your offer of help.
I suspect that my problem was due to me assuming that the null character (0) was handled in the asc and chr procedures I had found here.
In case it helps anyone else, I've modified the procedures to be robust to the null character (I hope!).

Test250ReaderEDIT.aia (206.4 KB)

The above project loads and saves - I have deleted the long ASCII strings. You need another way to handle them (are they actually necessary?)

See this post by ABG:

Many thanks for your help. I'll try uploading the revised project and study the post tomorrow. I look forward to using the updated version of AppInventor once it is released.

As you say, your edited version of my project loads and saves. MANY THANKS. You are a star!
I'll do further experiments with the Web component. It looks as if it will meet my current needs. Thanks for highlighting that possibility and another star to ABG for the lateral thinking of that work-around.
It would be nice to have Asc and Chr procedures added to App Inventor at some point in the future.

That is going to happen in the future - starting with some constants. One issue being that an empty text block looks the same as a text block containing a space char.

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