Could you please try turning off reader X protected mode and check if you continue to see the problem?
You could turn off protected mode using following steps:
1. Launch Reader X and select Edit->Preferences...
2. Select General from left navigation
3. Under application startup uncheck "Enable Protected Mode at Startup"
Note: You should switch "ON" protected mode after verifying the problem. Purpose of Reader X Protected Mode is to keep your system safe from PDF based exploits and keeping protected mode OFF will leave your system vulnerable.
What is the operating system you are using , your CPU speed , and What graphics card do you use.
Operating system: Windows Xp Sp3
The problem is on multiple machines so different video cards and CPU speed.
I checked two machines and they had an Intel(r) 82945G Express Chipset Family and a Intel(r) q965/q963 Express Chipset family
On the machines with the problem the Tahoma font wasn't correctly registerd, the file tahoma.ttf was installed in C:\Windows\Fonts but the registry key for the font was missing
Windows Registry Editor Version 5.00
"Tahoma Bold (TrueType)"="tahomabd.TTF"
After adding the registry keys a reboot was required to solve the problem.