Well not really. The system takes a little while to search for ads for you depending on several factors (Premium filter, gender filter, demographic filter, whether you have already clicked the same ad before, etc...)
Generally it takes about 2-3 minutes for the system to finish searching all the available ads for you. I personally view the Guaranteed ads right at the end because they will not go anywhere, since they are guaranteed. I start with the extra ads first in order of their pay rate (Extended > Standard > Mini > Micro) because many advertisers choose the fast delivery option so you have limited time to view them.
If you don't view the fast delivery ads within time, they might be allocated to someone else.
Most ads are allocated to an account for up to 1 hour. You don't really have to worry much about the warning for keeping the ads page open too long - "This Page Has Been Opened Too Long"
All you need to do is to refresh the page or click on the link under that warning box to refresh your allocated ads. When an advertiser purchases for example 1000 clicks those clicks do expire and can't be allocated to someones account forever. But refreshing the page ensures that those ads keep assigned to you.
So don't leave the View ads page unattended if there are ads available. Either refresh the page or simply click the available ads.
Above info was stated by the Admin here