task_pack.restrict_to_repacking() not working

Dear Sir or Madam,
I am learning the “Monte Carlo Side-Chain Packing” in Workshop6.

After successfully typing

task_pack = standard_packer_task(pose),

I was trying to use

task_pack.restrict_to_repacking() .

However, I was told “MemoryError” (attached). Can someone tell me what is the reason? Thank you very much.