Hi Venkateswaran,

I understand that you are not able to upload your class XII mark sheet for filling into the IISER application form and so to answer your question, firstly I ask you to check if this issue is due to some technical discrepancy by trying to upload the document repeatedly for 2-3 days and still if it persists then I suggest that you address this matter in writing through post to the respective authorities stating the entire matter in detail along with your proper credentials and data and request them to  rectify the discrepancy so that you can upload the document and also request them to expedite the entire process.