Not able to upload file in attachment field
Pankaj, open Archer's web.config file on the web server and search for maxRequestLength and see what it's set for. Ideally it should be set to 2097151.
If you do have to change the value make sure you make a backup of the filed beforehand and you'll have to do an IISRest and perform the same action all web servers running Archer.
In addition you may need to change IIS max Allowed content setting: https://community.rsa.com/t5/archer-knowledge-base/how-to-limit-the-file-size-that-can-be-uploaded-for-graphics-and/ta-p/614646
And you may need to check uploadReadAheadSize setting as well.