This article applies to TEKLYNX CENTRAL, and explains the problem of Print Preview failing to work because it cannot run SENTINEL, or SENTINEL is configured incorrectly.
When doing a print preview with the browser interface (AKA LABELNET), the image will fail to update and the “Error Failed to update preview” message appears. A default preview image will then be shown on the main browser screen. Sometimes, the fonts on that default image will be incorrect.
In order to generate a print preview, the browser interface uses the TCPrint or TCPrint Preview SENTINEL to generate the image. If it cannot run the SENTINEL or the SENTINEL is configured correctly, it will fail. There are at least four scenarios that we know can cause this problem.
SCENARIO 1: Cannot run the SENTINEL
The SENTINEL service needs to be started in Windows, it needs to be active on the SENTINEL Controller, and SENTINEL itself needs to be licensed. The two SENTINELs required are:
SCENARIO 2: TCPrint or TCPreview SENTINEL are not configured correctly
It one situation, we found the TCPrint and TCPreview were not using the “TEKLYNX CENTRAL preview” printer driver. Although the printer could be found in the “Printers” section of the SENTINEL CODESOFT Printing Plug-in, the “Load the printer saved in the label” setting was checked in the Options tab. This was apparently overriding the of the TEKLYNX CENTRAL preview printer driver. Since the label’s default printer or print driver was either corrupt or could not be found, the fonts were scrambled and the ‘failed to print preview’ error appeared. Unchecking the setting fixed the problem.
This time, the error appeared when the printer name had been changed in SENTINEL/CODESOFT, but the new name did not update in the TEKLYNX CENTRAL browser interface. Dropping the printer with the old name within the TCADMIN screen and re-adding the printer with the new name resolved the problem.
SCENARIO 3: Print Manager (SENTINEL) is too busy, Print User (LABELNET) times out
In this situation, repeatedly trying to do the print preview may resolve the issue. At the time, SENTINEL was running a different job (had been running for days) and we suspect the Print User (Browser) Interface just timed out waiting for a response from a sluggish SENTINEL.
SCENARIO 4: TC Preview Watch Folder Share is Not Working
For this example, we were not able to keep drop files from ‘getting stuck’ in the folder (SENTINEL would just say “Parsing” for the TC Preview). The issue was resolved by opening the properties on the Watch folder, selecting the “Advanced Sharing” button, selecting “Share this folder”, and adding “Everyone” to the permissions. After hitting “Apply” and testing it, we later removed the “Share this folder” option at it sill worked. Image is below:
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