First is an interrupt request (IRQ) conflict.  IRQ resources for PCI cards 
are assigned in the system BIOS.  The modem will use the IRQ value assigned
to the particular slot, so by changing the slot, you will change the IRQ of the device.

-Cause 2-

Make sure the modem is installed properly
Second is a memory range conflict with another device (usually video card).  Do the following
Start
Settings
Control Panel
Click on the system icon.
Click on the Device manager tab.
Click on the + in front of the HSF/HCF modem.
Highlight the Enumerator and click on Properties
Click on Resources
In the resource type area, you will see a Memory Range.  Highlight it.
Click off the checkmark from automatic settings
Beside Setting based on :Choose Configuration 0000 again. Even if it is there already
Click on change setting
Use the up and down arrows for the address and look at the bottom responses (No Conflict usually) 
Make sure it is at least 5 ranges away from the nearest device up or down.