Having received 100% success, ready for import, the next page then denies the upload, why? I have tried making the document smaller, only 700 entries, but receive the same OK then the same error. Please help!
This is going to be a version issue, I bet. Could you specify which version of Magento you are using.
For example, this will describe some resolutions released in 2.1.8 that may be what you need:
We’ve fixed an issue where product URL keys (for SKUs) were not auto-generated as expected during import.
More potential resolutions
In 2.1.3 CE Release notes:
Magento now removes category URL keys from the url_rewrite table as expected during import. Previously, Magento did not remove these keys, which triggered a failure during import. This subsequently caused Magento to quickly reach the maximum error count, returning this error: “Maximum error count has been reached or system error is occurred!”. (GITHUB-1471)
I just noticed you are showing version 2.1.12 ... Perhaps, check to see if any code from older core was retained throughout the upgrades?