I am getting following error while sending email to Emailservice

(Undelivered): 554 common.apex.runtime.ParseException  What would be the problem.

The code was running perfectly till last Friday 21-Mar-2015. I haven't change anything in code since then, but it's not working since two days; stange behaviour. Although even If I had any problem in my code, email should receive in Salesforce and then I can use debug log to see any code exception but I am receiving bounce back email with above error message.

Hello ,
         I have one object Project__c . In this there are one  picklist Assigned_To__c  in this picklist i add manually all user name. So whenever i choose for example Pritam Shekhawat then project owner should be Pritam Shekhawat. Give me a idea what is easy way to do this.
Thanks

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Basati:  We love smart people.  We're kind to everyone, but have no time to hand hold the average.  We pay well, offer benefits, have steady, full time work, interesting projects, and we maintain a zero hipster and NO creep workplace.  Oh, and we offer fresh, free coffee and periodic bagel days.



Learn more here http://bit.ly/hipsterfree or call me at 407-792-5692.  -Paul

Very frustrating.
SF team, please heed this suggestion.
Search is uselsess to differentiate between the two.
Could someone that actually has the ability to fix this please respond.
Thanks kindly.