A new update is available for SAS/STAT , version 14.1 :
PROC IRT issues WARNING: Factor scores cannot be computed for some of the observations
PROC IRT generates an incorrect score when the INMODEL(SCORE) data set contains only one observation
Note: A comprehensive list of all SAS hot fixes is available from support.sas.com. You can use the SAS Hot Fix Analysis, Download, and Deployment (SASHFADD) tool to manage your SAS hot fixes.