Thought limit upgrades usually require user verification such as SSNs and/or Bank details depending on your country? But again it probably also depends on the monthly limit you are asking for (i.e. USD 500, 2500, 10000), whether it is a limit on deposits or withdrawals and maybe even the nature of your account (I am just guessing here ).

One of the things you can try and do is simply google the exact error message you get and you should see an answer either from Paypal or another web forum. With Paypal's tens of millions of users, there is bound to be a couple of thousand that have experienced the same. But if you can attract Alma's attention (by starting a thread titled 'KDN is the best ISP' hahaha) I am sure he can provide a better response than I have.

By the way, drop me a line on AVLBLE.HERE(at)GMAIL(dot)COM for an offline discussion on a related matter.