This happens to me, too. it's been like this for years.
Thank you for reaching out to Constant Contact API Developer Support. My team is here to assist outside software developers with questions about building into Constant Contact's API.
I’m sorry to hear you’re running into errors while attempting to generate custom reports in our Events tool. As the Events tool is supported by our Tier 2 team, I will be opening a case with them to reach out to you within the next 4 business days. If you need a response sooner, you can reach out to our main support team using any of the methods on the following page and reference case #30241855.
Constant Contact Support:
Please have a look and let us know if you have any other questions!
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