The propane gas line can have air in it. I had a similar problem with the propane gas stove at my rental not lighting after being unused for several months. The air just needed to be purged from the line.
But, please be careful! My husband had a propane grill ignite with quite a "boom" because spiders had spun a web in the gas line. (He wasn't hurt, thankfully.) The webs block the gas line, the gas builds up and then there's a flash fire when it finally ignites. I don't know if the same thing can happen with a gas fireplace, but better safe than sorry!
There are lots of possible reasons. As wildiris says, air can accumulate in the line.
Start with the obvious and easy -- is the valve at the tank turned on? Are all inline valves turned on? Is there propane in the tank?
I infer that you removed the orifice at the fireplace end to clean it. Can you see light through the orifice hole? If not, a pin might clear it.
If a fixed pipe is used for the propane supply there probably will be a moisture trap in the pipe. It is usually a short length of pipe extending down from the main line with a cap on the end. You could unscrew the cap to drain any water that has accumulated. Be sure the valve is turned off at the tank when doing this, and if there is a valve past the moisture trap turn it off also. While the trap cap is removed open the tank valve briefly to check for the odor of propane indicating it is flowing out of the tank. When screwing the cap back on, use teflon tape intended for use with gas lines--it is normally yellow while the tape for water lines is normally white. To ensure the cap is securely screwed back on use a soapy water solution to check for bubbles, don't just rely on your nose to sniff for the odor of the propane.
There may be a problem with the pressure regulator at the tank. You might try tapping it with a hammer.
There may be rust or debris accumulated in the line. It may require removing fittings at both ends of the line and blowing it out.
Wildiris and Sage, thank you for both for your wise counsel. After reading what both of you wrote I decided to just go ahead and call the fireplace company. Sage I remember the incredible help that you gave me on the recliner repair (and its still working just fine) but dealing with propane just makes me a little uneasy. I called the company today and they are to call me when they can get me on their schedule LOL!! That tells me I am not the only one dealing with issues on their fireplace.
So, while I have always been a do-it-yourself kind of gal when it comes to propane and possible danger as it relates to it, I did what I could and now the experts who know exactly what to do without blowing up my house will have to complete the task.
I Appreciate the two of you so much for always trying to help me with my little Vacation Rental issues when I am sure that you both have better things to do.
10 years now and feel like we are definitely old friends for sure.