now I know why I had this error, when I'm accessing the thing's property from inside a sub-thread, I have this error, but if I access it from the main thread of the Resource it goes without errors. So, as carlos said "If you create a sub-thread you may need to initialize Security Context for the newly created transaction" and here we have an example for that https://community.ptc.com/t5/ThingWorx-Developers/Running-another-thread-in-the-Thingworx-Extension/td-p/528607
now I know why I had this error, when I'm accessing the thing's property from inside a sub-thread, I have this error, but if I access it from the main thread of the Resource it goes without errors. So, as carlos said "If you create a sub-thread you may need to initialize Security Context for the newly created transaction" and here we have an example for that https://community.ptc.com/t5/ThingWorx-Developers/Running-another-thread-in-the-Thingworx-Extension/td-p/528607
Glad to hear you found a solution. It would be helpful if you could mark your post as the Accepted Solution for the benefit of others with the same question.
