Perform a search of the drive for files in excess of 10,000 KB in size. Review the results to determine if any of the files can be deleted. In particular, look for Equitrac log files. Logging should only be enabled when troubleshooting an issue. If left enabled, the log files can quickly grow in size and fill the drive.
Please refer to knowledgebase article 19519 for a discussion on calculating the minimum free space required to accommodate your Equitrac secure print queue as configured. This minimum is over and above any Microsoft server free space requirements.