Received length does not match 33 error on compile in PROS

Whenever I try to compile my program using PROS, the following window is pulled up with “received length does not match 33”.
(Apologies for the highlighted text.) After this error appears, PROS is no longer functional and the window cannot be closed. I’m running CLI version 3.1.4

Read this entire topic.


Nothing I found there seems related to the issue I’m having and the fixes presented did not help.

You said.

and the error you are showing implies you have a V5 on vexos 1.0.13. is that the case ? If so that version of the cli is not compatible.


Updating seemed to have fixed that error (someone on my team updated without me knowing) but I’m now having another issue. Opening api.h reveals this.
This is the error on compile.

This error is addressed in the PROS CLI 3.2.0 release Known Issues: PROS CLI 3.2.0 - 📶 Wireless Terminal! (IMPORTANT)

If I remember correctly, you have to add the ARM GCC toolchain to your system’s path. Instructions on how to do so are in the post I linked.

Also, the errors you’re getting on the #include statements are probably caused by the linter (see this post). They aren’t actual errors in the code, though, so you should be able to compile.


The fix here doesn’t seem to be doing anything (assuming I’m doing it correctly). It is also not a linter error as the compile fails with the error in my above post.

Have you done this per the instructions ?

UPDATE : if you are unable to build projects, please add %PROS_TOOLCHAIN%\gcc-arm-none-eabi-10-2020-q4-major\bin to your PATH environment variable

That’s exactly the compile error you are getting, make cannot find g++

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This is the config I have for it.

I don’t see the user variable PROS_TOOLCHAIN

@Hotel @RanchSauce can we get this windows installer fixed ?


There is an entry for PROS_TOOLCHAIN under system variables.

What happens if you open Windows command prompt and try to run arm-none-eabi-g++ manually?

Also, do you even see the file in the bin folder?

Finally, do you have multiple distributions of Python installed on your system? (that could mess with PROS)

At this point I would:

  • uninstall everything PROS related
  • uninstall Python
  • check that you don’t have any Python or PROS related system or user environment variables
  • reboot
  • reinstall Python
  • reboot
  • reinstall PROS, following this procedure: PROS CLI 3.2.0 - 📶 Wireless Terminal! (IMPORTANT)
  • create new project, compile it, and upload to V5
  • only then import your code into that project and try again

I did some messing around with it last night and managed to get it to recognize the CLI. However, whenever I try to compile I get the following error.
When using quick action, PROS does not compile the project and just uploads the previous hot package. Wireless upload is also not working, giving the following errors.
I have added the path variable mentioned in the PROS release post (PROS CLI 3.2.0 - :signal_strength: Wireless Terminal! (IMPORTANT)).

This is a seperate issue.

Oh I assumed this was what they fixed in 3.2.1, but apparently not.

fixed in 3.2.1 yes, but not



I can build now, but I’m still unable to upload. It always says that no v5 ports are found:
This has happened to me across multiple PROS installs (on different computers), multiple cables, and multiple brains.

Have you ever been able to upload with that particular cable? Some micro-usb cables only carry power, and cannot sustain a data connection to the brain. I don’t know if this can be visually inspected, so I would suggest trying different cables.

Alternatively, you could use check if the port on your computer is working but testing other USB devices.

Any testing that you can do and report back on will be really helpful

edit: I just realized you posted a new topic for this issue so all further comments regarding the “unable to upload issue” will be addressed here.