Images do not load on fast connection

[YanY1]

I have created a web control that shows the list of available files in a datagrid on an aspx page. Depending on the file extension, I am changing the little graphic for each line in the datagrid to the corresponding filetype (Ex. pdf, doc, xls, etc.). Control is working fine if the connection to my site is not too fast. Otherwise images do not show. If I right click image and choose Show Picture option, all of the images load fine. Again, if I am using Cable Modem connection or local server (fast) pictures do not show, if it modem or slower connection -- control renders just fine. I have tried using Response.Buffer = True but it does not help.

Any suggestions are greatly appriciated. Thanks in advance.