I have now attempted to push this repo, which no longer contains any reference to a sub repo, up to a completely different installation - new project, new repo.
The sam error occurs. I'm not sure the issue is the sub repo - but I'm a little stuck.
Can someone help?
The repo contains about 2GB of images and unfortunately, a large majority of these were pushed in a single changeset.
In case anyone else has the same problem:
I resolved this issue by updating the content length allowed in the IIS settings for the site.
Specifically increasing the maxrequestlength of the httpruntime settings and the maxAllowedContentLength in requestFiltering.