Since this is an Info*Engine error, you might also want to delete the compiledTasks directory under <wt_home>/tasks/com/infoengine. This will ensure that all cached infoengine webjects are recompiled and re-cached.
Thanks
Alexius C. Chukwuka
IT Analyst, Global SAP Basis - TCM
Deere & Company World Headquarters
400 19th St, Moline, IL 61265