I was wondering if I have to use special RNA loading dye or can I run RNA samples with regular loading dye that is used for DNA?
Handling of RNA requires extra care, especially using RNase-free pipette tips, tubes and reagents, to prevent RNase contamination. Common labware and reagents usually indicate whether they are RNase-free certified. If there is no such mention written on the box or label, then you should assume it is not RNase-free and you should not use it to handle your RNA.
Check whether your loading dye is certified RNase-free (this should be written on the tube, or easy to find out on the manufacturer's website using the product reference number). If it is, and you exclusively used RNase-free certified tools and reagents all the way, then maybe the loading dye tube or something else got contaminated by one of your co-workers.