Error -251927 When Uploading Tags From LabVIEW

Issue Details

I am using the LabVIEW SystemLink Toolkit to write 30 tags every 5 seconds. However, I sporadically encounter the following error while the code is running: 

Error -251927 occurred at NI Skyline Utilities.lvlib:Parse HTTP Error.vi:5080001
Possible reason(s):

Too many tag values were written in the last second. By default, one thousand tag values may be written per second. Retry your request after a short delay, or with fewer values.


Complete call chain:
NI Skyline Utilities.lvlib:Parse HTTP Error.vi:5080001
NI Skyline Utilities.lvlib:Execute HTTP Verb.vi:7500001
NI Skyline Tag HTTP Library.lvlib:Multi Write Core.vi:5310001
NI Skyline Tag HTTP Library.lvlib:Multi Write.vi:4780001
NI Skyline Tag HTTP.lvclass:Multi Write HTTP 2.vi:1870001
NI Skyline Tag.lvclass:Multi Write 2.vi:6740001
Write Array of Tags.vi

Solution

As the error message says, the reason for this error is that you're reaching the limit of tag writes per second. One of the reasons for it might be hidden in your code. For example, when writing multiple tags, you should first create an array of clusters containing tag information using the Generate Tag Cluster.vi, to then write them all at once using the the Multi Write.vi. If this array grows unexpectedly, you'll eventually get the error -251927.

The code snippet below shows an example of an accidental uninitialized shift register that is causing the tag array to indefinitely grow up at every while loop iteration increasing the value of Number of Tag Values to be Written indicator increases.

 

In this case, the solution is to initialize the shift register with an empty array constant. If you do that an monitor the value of Number of Tag Values To Be Written, you'll see it remains constant, which is the expected behavior.