Am calling it from 32-bit Matlab, but thanks for the comment.
To resolve the issue, I had to set the path argument of the treikon function to a folder that contained 6 required dlls.
c = treikon('IDN',... 'C:\Program Files (x86)\Thomson Reuters\Eikon\X\Bin')
In my installation of Eikon, these 6 dlls were contained in 2 different folders. So I copied 2 of them into the folder that had 4 of them ie to C:\Program Files (x86)\Thomson Reuters\Eikon\X\Bin.
FYI, the required dlls are Interop.EikonDesktopDataAPI.dll, Interop.AdfinXAnalyticsFunctions.dll , Interop.AdfinXAnalyticsObjects.dll , Interop.Dex2.dll , Interop.RSearch.dll , Interop.RTX.dll
