It is generated by the ASPNET_regiis /c command. Most websites I use have ended up including this in the distribution because the sys admins always forgot to install it. It contains the client side JavaScript libraries required by .NET1.x to handle the postback eventing model on the client side.
You can delete it if you have upgraded to .NET 2 which uses a different handler for the scripts (or if you are prepared to recreate it.) But check first that there aren't additional files added there by the author as sometimes I have seen it used for extra stuff.
与恶龙缠斗过久,自身亦成为恶龙;凝视深渊过久,深渊将回以凝视…