Go to the folder containing your catalog and delete the folder with the extension .lrdata. Then start Lightroom, and it will begin creating a new cache file.
Sorry for the late reply...
I did just as you said and it worked. Thank you for your help mate!
I'm glad that worked for you. Just another observation. Splitting the catalog because of size really shouldn't be necessary. The catalog is just a database. I think you will find it much easier to manage your images with just a single catalog. But the choice is yours. Technically speaking, there is nothing wrong with having multiple catalogs. But it seems to complicate things when trying to find images.
Lightroom is causing my computer to hang lately. It is extremely slow to work with!!
I thought is was because of the 22k odd photos that I have archived already.
I thought that it would be simpler if I split my main catalogs into Wildlife and Aviation respectively. This is about all I shoot.
Also I use a Pentax K50 which only shoots in DNG. The majority of these photos keeps having errors on Lightroom. I believe that the error is to do with building "Smart Reviews". In addition I also shoot with a new Pentax K3. Some of the photos don't even show on Lightroom, even though the camera body displays them..????
Have you any advise for this. I recently upgraded to a USB 3 port thinking that it would speed things up. But it has made no difference.
Generally speaking, the size of the catalog should have no impact on Lightroom performance. To my knowledge, Lightroom should support the DNG files from your Pentax cameras. When you say that "some" of the images won't even display in Lightroom, that is an indication that you have a problem either with the card, or the camera, or the hard drive where the images are stored. If you aren't already, I suggest that you use a card reader to download your images.
I do use a card reader. But I think that this warrants a upgrade to something more substantial now.
I use a basic Lexar Card reader, I managed to get most of my images imported, but like I said maybe some investment will solve the problem.