Gives the stated error when I try to link schematic to the layout.
I had this issue and it was related to me pinning the application to the taskbar in Windows. From the support site:
PADS VX.0 and later
When starting PADS Layout from the Start menu the program launches with a wrapper script that automatically configures the correct environment variables. The proper launch file is located in C:\MentorGraphics\PADS[version]\SDD_HOME\common\win32\bin\powerpcb.exe.
However, if PADS Layout is launched directly from ..\SDD_HOME\Programs\powerpcb.exe then the wrapper is not launched and the proper environment is not configured. When attempting to connect to xDX Designer by clicking on the Connect button in the xDX Designer link the application will fail to connect with the "Error opening iCDB". If xDX Designer is not open already you may receive the message "xDX Designer instance can not be created".
The problem can also be created when PADS Layout is running if you right mouse click and choose "Pin this program to Taskbar". The shortcut it defines on the Taskbar is directly to the ..\SDD_HOME\Programs\powerpcb.exe, which by-passes the wrapper script. If you would like a shortcut on your desktop or on the taskbar then do the following:
If you are launching PADS Layout from a non-standard shortcut icon and experiencing the "Error opening iCDB" when clicking Connect in the xDX Designer Link try restarting PADS Layout using the icon located in Start > Programs > PADS [version] > PADS Layout and then connect to the project using the PADS Designer Link.
If you are still seeing the message "xDX Designer instance can not be created" after launching from a proper shortcut icon the please do the following:
Opening an Integrated project PCB file
If an Integrated Project pcb file is launched from a non-standard shortcut this will pop up the error message "iCDB opening failed: Database cannot be loaded and the server cannot be started, the project will not be opened. Please use iCDB Project Backup 'Repair project' functionality to fix this issue." Close out of PADS Layout and relaunch it using the shortcut in Start > Programs > PADS [version] > PADS Layout and then load the pcb file.
Any iCDB Version
The KEY iCDBDir is incorrect in prj file.
The "error opening iCDB" can occur when attempting to connect to DxDesigner using the DxDesigner (xDX Designer) Link in PADS Layout when there is an incorrect entry in the prj file for the KEY iCDBDir entry.
Create a copy of the prj file for safe keeping. Manually edit the prj file in an ASCII editor to change the following line :
KEY iCDBDir "database"
KEY iCDBDir ".\database"
Retrieving data ...