Hi,

if my memory is correct, i might have faced this issue a few month ago. in the log, i can see this

searched 14 extensions in file /Users/krish/Library/Application Support/Astrometry/index-4204-13.fits but didn't find a table with a column "kdtree_perm_stars".
searched 14 extensions in file /Users/krish/Library/Application Support/Astrometry/index-4204-13.fits but didn't find a table with a column "kdtree_bb_stars".
searched 14 extensions in file /Users/krish/Library/Application Support/Astrometry/index-4204-13.fits but didn't find a table with a column "kdtree_splitdim_stars"

it happened when i pasted the index files in the folder (from a backup) instead of downloading them from the Align option window. If you had downloaded them, i am wrong and i don't what happens there. Maybe some more experiment users may answer better or propose some others solutions.

Val
 

Thanks Val
I did a clean install of KStars and downloaded the index files, so not copied from previous versions.

IIRC, you need the GSC catalog to solve with the simulator. Could you have forgotten to install it on your iMac?

"sudo apt install gsc"

Thanks Gilles
I have loaded the gsc files through Kstars wizard. The gsc folder is in the Kstars folder on both machines.
I tried it a few times last night, with some higher exposure and gain settings. It will solve sometimes and sometimes not even with the same settings that did work. It seems to be very erratic.

Could someone please give me an indication of where all the KStars/Ekos related files and folder are on MacOS.
I have located a few from other posts and have deleted them before doing the last re-install. I may have missed something and want to try the re-install.
 

Go to your home folder in the finder and press Shift+Cmd + . to see all hidden files. All you need is in

~/Library/Application Support/kstars

Here you find the folder gsc containing the GSC catalogue, folder darks and defectmaps containing any captured dark frame information, astrometry containing all the index files and analyze with the analyze files from your last sessions. Also your settings database in userdb.sqlite including a backup file from this (and you should store this file as a backup somewhere else to have another copy if you need it later). Don't remove other files from here unless you plan a reinstallation.

I already installed KStars twice on my Mac to resolve nearly the same issue, but it did not help. Maybe you have more success.

A common issue with the simulator is not setting gain. Set gain to 100 and try again, do you see any stars?

Thank you all for the suggestions.
I played around this afternoon and before starting a solve on the iMac I checked all the settings between both machines. I found that the FOV in the align module was different to what I found on the MacBook. For some reason it seemed different this time with the simulation camera on both machines set the same. Toggled between guide camera and primary and stil had the same wrong setting. I have check settings before and don't remember seeing it different. After setting it the same as the MacBook solver worked and has worked every time since then.
Changed camera settings and the align module updates the value correctly every time as well.
I have not had to change any other settings. Exposure @ 1s and no Gain --. Solver works on both machines with these settings.
Now going to run 3.5.4 on the iMac. Hopefully all still goes well after that. MacBook is still on 3.5.3.
Thanks again to everyone.

Unfortunately 3.5.4 did to work. Solver tries to solve but fails with too many attempts.
The Solver FOV and Simulator FOV are on the target. Error is showing greater than Accuracy setting but the mount does not seem to do anything.
I have reverted back to 3.5.3. 
Will try 3.5.4 some time in the future.
Will try the live version when weather permits and the moon is out of the way.

 I decided to give 3.5.4 another go, but still fails to solve.I think it has something to do with the error in the solution error calculation.The error in the solution coordinates and and the reported information is different. Somebody can perhaps make sense of it and help with a solution to the problem.
See attached screenshot

After playing around with 3.5.4 to try and get solver to work and now 3.5.5 solver is now behaving erratically. It will solve on very few occasions and most times it will just continue to slew and solve until I stop it.
Could someone please take a look at the log file to try and help me identify what I may  have set incorrectly.
I have deleted all that I could find of any previous files associated with KStars before loading 3.5.5.
I am doing this with simulation.
I have attached the log file and screenshots that show target in centre and one of the Align module. I also have a screen recording if someone would like to look at what I mean by continue to slew then solve.
Please let me know if there is anything I can provide that may help identify the problem.Thanks