Invalid mode/filename error when assuming IAM role for cross-account S3 access #1063

Another AWS account has data in an S3 bucket that I would like to access from my AWS account. We followed the instructions from the AWS CLI talk at re:Invent 2014 for cross-account access using the CLI. We created the role s3CrossAccountAccess from the AWS console and added an entry to the config file for the assumerProfile profile:

[profile normalProfile]
region = us-east-1
[profile assumerProfile]
role_arn = arn:aws:iam::xxxaccountidxxx:role/s3CrossAccountAccess
source_profile = normalProfile
region = us-east-1

When I run aws s3api list-buckets --profile assumerProfile I get the error below. It also creates an empty folder at C:\Users\username.aws\cli\cache.

[Errno 22] invalid mode ('w') or filename: u'C:\\Users\\username\\.aws\\cli\\cache\\assumerProfile--arn:aws:iam::xxxaccountidxxx:role-s3CrossAccountAccess.json'

I'm using version 1.6.9 of the CLI for 64-bit Windows.

Any ideas what I'm doing wrong, or if this is maybe a bug in the CLI? It looks like it's trying to create an improperly named file.