Steps to reproduce
1. Open attached project.
2. Notice that window "API Update Required" appears automatically.
(if this window does not appear, click "Assets"->"Reimport All" and it should appear)
3. In this window press button "I Made a Backup. Go Ahead!".
4. After project is loaded, notice error messages in console window: "Failed to run script updater", "API updating failed". Also, it suggests reporting a bug with details provided.
5. Open script named "BloodSplat.boo" and temporary delete this line of code:
safeLength as int = pSystem.safeCollisionEventSize;
6. Reimport assets of this project ("Assets"->"Reimport All").
7. Notice that error messages about API updating disappear.
8. Write the same line of code to its previous location in "BloodSplat.boo" script:
safeLength as int = pSystem.safeCollisionEventSize;
9. Reimport assets and notice that API updating failed.

Expected result:
Scripts should be updated without any failure. "safeCollisionEventSize" should not be a barrier to run script updater.

Reproduced on:
5.3.4f1, 5.4.0b13, 5.2.4f1, 5.1.0f3.