Workflow stuck in starting status

I have a workflow that uses a third party component to generate a PDF and save it in a SQL database. It does so by making an http request to gather the html that will be the content of the PDF. 

I simply add and employee ID and a template ID into a SP list, and the workflow uses these on the query string of the url for the request to generate the PDF. It's quite simple really. If I paste 15, 20, or even up to say 35 items into a datasheet view of this list, the workflows kick off and everything is fine. I want to paste about 1800 though. When I do so, I get about 140 (this varies really) PDFs generated and then I have a bunch of them stuck in starting or pending or processing. It seems like something just crashes. The http request is to a custom sharepoint page, btw. The whole app is done in vs 2010.

This has not been tested on a server and perhaps I should go that route, but I wanted to get it working on my local Win7 environment first.

Any help would be grealtly appreciated.