The PayPal system is designed to drop your connection, or 'time out', after five minutes of inactivity.
It is usually a cookies issue on their computer. Send these instructions for them to use:
If the system is timing out in less than five minutes, it may be due to a loss of secure connection, which is usually caused by net congestion
If you do not clear your cache files periodically, you may experience longer loading or browser closing times. In order to improve your performance on the web and specifically while visiting our site, we suggest that you occasionally clear your cache.
Below are instructions to clear your cache for various browsers. If your browser is not listed below, we suggest that you use the help section of your browser or contact their customer service center.

Internet Explorer
1. Click the 'Start' button'
2. Select 'Settings' and click 'Control Panel'
3. Double-click Internet (or Internet Options) and select the 'General' tab
4. Click the 'Settings' button in the Temporary Internet Files section and choose 'View Files'
5. Click 'Edit' and select 'Select All'
6. Press the 'Delete' key on your keyboard. If prompted to verify that you want to delete your cookies, click 'Yes'

Netscape
Your computer stores copies of frequently accessed pages in the memory cache or disk cache. This way, the computer doesn't have to retrieve the page from the network each time you view it.
To set the size of the memory cache or to clear it (Windows and Unix only):

1. From the 'Edit' menu, choose 'Preferences'
2. Open the 'Advanced' category and click 'Cache'
3. To clear the 'Memory Cache' immediately, click 'Clear Memory Cache'

AOL
1. Open the AOL account
2. Click the 'Settings' button on the toolbar, ('My AOL' for older versions)
3. Select 'Preferences'
4. Select the 'Internet Properties (WWW)' link on the left-hand side,
5. In the middle of the Internet Options box is a section called 'Temporary Internet Files'
6. Click 'Delete Files'. Place a check mark in the 'Delete All Offline Content Box'
7. Click 'OK'

Please Note: If you are attempting to write a long description when sending a payment or Money Request/Invoice, we recommend opening a text document, typing your message, then copying and pasting it into the PayPal page.
I understand your frustration regarding this matter and apologize for any inconvenience it might have caused you.
Sincerely, Pat PayPal Customer Service PayPal, an eBay Company