The regex too complicated message is based on the size of the file that you are trying to schedule via the Report Scheduler.  Because the Report Scheduler attaches your scheduled report to the Notes & Attachments related list on your Scheduled report, the report size is subject to Salesforce limitations. Your report is pushing a data size that far exceeds the heap limits. The regex seems to be failing because of the heap supporting the regex. The only alternative is to analyze your report and see how you can leverage filters, to reduze the number of rows to less than 2,000.