ERROR - Guard::RSpec cannot open results file: tmp/rspec_guard_result

[pas256]

I just started getting this after successfully using Guard for months

10:46:06 - INFO - Running: spec/models/sheet_spec.rb

Randomized with seed 50436
.................

Top 2 slowest examples (0.17682 seconds, 66.5% of total time):
  Sheet#row_order_map returns a hash of row IDs and their order
    0.15959 seconds ./spec/models/sheet_spec.rb:145
  Sheet#name is automatically generated and unique if not provided
    0.01723 seconds ./spec/models/sheet_spec.rb:27

Finished in 0.26588 seconds (files took 2.06 seconds to load)
17 examples, 0 failures

Randomized with seed 50436

10:46:09 - ERROR - Guard::RSpec cannot open results file: "/Users/.../tmp/rspec_guard_result". This is likely a bugso please report this at http://github.com/guard/guard-rspec/issues/new along with as muchinformation as possible to reproduce this issue.
10:46:09 - ERROR - Guard::RSpec failed to achieve its <run_on_modifications>, exception was:
> [#] Errno::ENOENT: No such file or directory @ rb_sysopen - /Users/.../tmp/rspec_guard_result

If I load Guard and run all the tests, this does not happen, but when I save a file (in this case sheet_spec.rb) and guard runs just those tests, this error message appears at the end.

I'm happy to help debug this. What else would be helpful?