Non-residential tax liability - Indiana

My total income earned last year was around $7800.   I was living in Illinois but was working in Indiana.  I actually worked for (meaning actually at my place of employment) less than 30 days.  I filed my Indiana state tax return and they said they were unable to verify this and only sent me a portion of my expected refund.    A representative from the DOR in Indiana said that this was because I wasn't working for a company in Illinois who sent me to Indiana to work.   I researched Indiana DOR Bulletin #28 and could not see how I didn't meet their eligibility requirements.