Can you send a screenshot of what you are seeing? My assumption is that you are seeing PHP Ajax Datagrid 1.4.9 listed in your My Stuff section but it is not giving you the option to update - is that correct?
If yes then please search under the All section for PHP Ajax Datagrid. Complete the steps to purchase the extension however it should prompt you that you have already purchased the item. Click OK and it should start to download and install version 1.4.10.
Please send an email to fgregor at adobe dot com if this does not resolve the issue.
Tried that and it tells me that I already purchased but it will not update. BTW - the plugin now has version 1.4.11 and I still cannot update!!!
FYI - When the dialog box come up to tell me I already purchased the plugin it has "error" for the title. The developer keeps telling me he will not help me... I purchased through Exchange so I have to update through Exchange.
Did your issue get resolved yet? If not please message me directly.