Just opened a project from a couple of months ago and I got a Error running platform build action hooks.postbuild when compiling for a Teensy 4.1. Any ideas?

Please find the build properties listing attached.

Kevin

The build looks good. The hook message can be ignored. Build hooks can cause warnings when they attempt things such as encryption, when encryption is not configured. The last potentially more important message says your program size is too large.

teensy_size: Memory Usage on Teensy 4.1:
teensy_size:   FLASH: code:397776, data:156336, headers:9084   free for files:7563268
   RAM1*: variables:174368, code:394752, padding:31232   free for local variables:-76064
teensy_size:    RAM2: variables:24928  free for malloc/new:499360
   Error program exceeds memory space

What is the error you are seeing? The build process is defined by the platform.txt in your "AppData\Local\Arduino15\packages\teensy\hardware\teensy\avr" folder. (nb: The 'avr' part of the path is how teensy works and does not relate to mcu type) 

You would expect to see this message "No key .pem file found, skipping .ehex encryption" because the platform.txt attempts to encrypt the hex if a key file exists. The command is defined as "recipe.hooks.objcopy.postobjcopy.1.pattern=" in the platform.txt

The memory usage is determined by running the "recipe.hooks.postbuild.3.pattern=" in the platform.txt. That uses it's own teensy_size.exe to determe the size of the memory limit for the program code to be valid. You can see this defined in the platform.txt.

Teensy is unique in the fact that when you build it also runs (or attempts to run) the upload tool. This means that whilst you only wanted to build, the fact is that is no different from build and upload. Teensy has always worked this way. This is also defined by the platform.txt build instructions.

Are you reporting that the teensy memory usage reporting is showing the error? If so, do you see same in the Arduino IDE?