I have a post-receive hook that is running as user \'git\'. I have a virtualenv /python/ve//bin/activate that is readable by git. Running:
source /python/ve/
This is something of a guess, since you haven't quoted your complete post-receive hook, but I suspect that you don't have a shebang line pointing to /bin/bash at the top. Your post-receive hook should begin:
#!/bin/bash
I suspect this because if I run a strict Bourne shell, like dash, I get the same error when trying to source anything with source.