The login screen coming up is likely causes by the inactivity timeout for ACT! for the WEB. While the report is compiling there technically isn't any activity from the remote user so when the inactivity time period is reached, it would abort. A couple of things to try, see if the report will complete when run from the server. If it fails there then there may be problems with the database and you should do both the regular maintenance and the reindex from ACTDIAG.