The standard settings for Reporting in SageCRM are not sufficient. We repeatedly see issues with reports failing to preview or print. My advice is to change these settings in the Documents and Reports Configuration.
Reports query timeout - increase to 120 from 60.
Reports build timeout - increase to 120 from 60.
Reports Admin override - set to Yes.
Desktop Size Limitation (Kb) - set to 10000.
Try these for starters and increase as needed. Good Luck and good reporting!