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Invalid driver warning - Deleting a modifier or constraint with a driver still active produces persistent warning
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Description

System Information
Operating system: Windows-10-10.0.19041-SP0 64 Bits
Graphics card: NVIDIA GeForce RTX 3070/PCIe/SSE2 NVIDIA Corporation 4.5.0 NVIDIA 465.89

Blender Version
Broken: version: 2.93.2 Release Candidate, branch: master, commit date: 2021-07-07 05:52, hash: rB9e64fd461ac3
Present in all version I've tried, from 2.93.0 to current (21-07-12) 3.0 Alpha

Short description of error
Deleting a modifier or constraint with a driver still active produces persistent warning:

anim_sys.c:3132 BKE_animsys_eval_driver: invalid driver

To get rid of said warning, which persists between sessions, you have to recreate a modifier/constraint of the same type, (which will then still have the driver present), delete driver, then delete the modifier/constraint. (Or delete object)

Really pernicious warning, since it references a modifier/constraint that the user has deleted and can't find anymore.

Exact steps for others to reproduce the error

  • Create modifier/constraint
  • Create a driver which drives a value in modifier/constraint
  • Delete said modifier/constraint by clicking the X icon on said modifier/constraint

Event Timeline

This is essentially the same as T89679: Animation channels do not get removed from action when according modifier/constraint is deleted, please read T89679 for design considerations.
In short: this is not considered a bug, will merge these reports.

Ive noticed this same behavior when i opened a file created in bl2.93.5 from windows on my osx machine using 2.83. I know it warns me for compatibility and such, but seeing this issue has been stated couple times here in devtalk. I thought i would add this comment.

What i noticed is that when i preview the bend modifier in the 3dview all looks fine. But when i do a render or animation render, then i see this warning.

Same as @Marcus Krupa (kerfuffle) stated, only way to salve this is to delete all drivers and rebuild everything. Not really ideal! But i guess this would be seen as a backward compatibility issue perhaps. Im not sure if it the modifier being different though. The error is about the driver, but that driver menu looks exactly the same as on 2.93.5