Troubleshooting the image cache

This topic provides information that may help you to resolve problems that you come across when using the Image Cache.

If the pages of the interview are returned with a white background and do not use the specified template, then the Web Service was unable to load the template file. Whenever the Web Service is unable to load a template, it writes an error message to the IVW log file on the Web server. By default, the IVW logs are stored in:

[INSTALL_FOLDER]\IBM\SPSS\DataCollection\<version>\Interviewer Server Administration\Logs

The first step when debugging a template issue is to locate the log entry for the error. The main reasons why a template cannot be loaded are as follows:

Templates must be written in well-formed XML. Put simply, this means that every tag must have an opening and a closing tag so, for example, you must always write <br/> rather than just <br> to create a line break. If the XML in your template is not well formed, you will see a parsing error in the log files. For example:

Error parsing template
'http://SVR1/SPSSMR/ImageCache/ImageCache.aspx?Project=englishmuseum&File=Card_Blue.htm', line 33:
End tag 'TR' does not match the start tag 'TD'.

If the Web Service cannot load the template, it writes an error message detailing the Project and Global locations that it used to locate the template. For example:

Unable to load template 'Card_Blue.htm'. Using default template.
Project location='http://SVR1/SPSSMR/ImageCache/ImageCache.aspx?Project=englishmuseum&File='. Template location='[INSTALL_FOLDER]\IBM\SPSS\DataCollection\<version>\Interviewer Server\Server\mrIWeb\Templates\'.

The first step is to confirm the template cannot be loaded by testing the Image Cache URL in a browser on the Web server. For example, type:

http://SVR1/SPSSMR/ImageCache/ImageCache.aspx?Project=englishmuseum&File='card_blue.html

into the Address box in the browser. The error in the browser should give some indication as to why the file cannot be retrieved. One common problem is that the Web server does not have access to the Master project folder. In this case, the Image Cache needs to be configured to load images from a remote Image Cache. See How to configure the image cache for more information.

Another common scenario is that the Web server cannot resolve the server name in the file's URL. Try replacing the server name with "localhost" or with the computer's IP address.

Once you have a URL that works, change the LocalImageCache setting in the Web Service's configuration file (see How to configure the image cache). You must reset the Web server to pick up the new configuration setting. See Resetting IIS for more information.

If templates are being displayed but the images specified within your interview script are not, then the Image Cache URL is probably configured incorrectly. To test the Image Cache URL, extract the URL from the src attribute in the interview HTML source and test the URL from an external client computer. For example, type:

http://svr1/SPSSMR/ImageCache/ImageCache.aspx?Project=englishmuseum&File="Image1.gif"

into the Address box of your browser. Remember to replace &amp in the src attribute with just &, as shown here. The error in the browser should give some indication as to why the file could not be returned.