Problem Resolved.

It seems that this error is caused by there being a difference in the ‘Time out’ between datasets, whilst the main dataset was set to 500 seconds the dataset which holds the Attribute formats was set to zero.

As a random test I changed this dataset to 500 the same as the main dataset and the above error disappears, also changed them both to zero seconds and that also resolved the problem. (The code wasn't exceeding 500 seconds, it in fact only took about 30 seconds in total) 😀