Please follow below steps to take care of environment variable settings and other settings to over come the error.
1. Right click on My Computer->Properties->Click on Advanced Tab->Click on Environment variables(at the bottom)
2. Environment Variables window will be opened-> In the you will find “USER VARIABLES” as shown below: Click on New as marked
3. In the pop-up window set variable name to TCLLIBPATH and value to "C:/Program Files/Spirent Communications/Spirent TestCenter 4.00/Spirent TestCenter Application"
4. Click OK.
Follow the below steps if you have not modified the pkgIndex.tcl file.
1. Open Spirent TestCenter Application folder. Path to open the folder is “C:\Program Files\Spirent Communications\Spirent TestCenter 4.00\Spirent TestCenter Application”
2. You will find pkgIndex.tcl file. Right click and open with notepad.
3. Please edit the file as shown below with red marked rectangles:
4. Set STC_INSTALL_DIR to “C:/Program Files/Spirent Communications/Spirent TestCenter 4.00/Spirent TestCenter Application”
5. And also modify the STC_INSTALL_DIR with $STC_INSTALL_DIR as shown in the screenshot above.
I hope the explanation with screenshot helps to set the environment variable and to edit the pkgIndex.tcl file.
Once the settings are done, you will find output of auto_path as C:/Program Files/Spirent Communications/Spirent TestCenter 4.00/Spirent TestCenter Application
NOTE: This is for Version 4.00. Same steps can be followed with other versions also but make sure that you are doing changes in correct files with respect to version.