What version & SP are you using? I see this all too frequently on 2015 SP 5.
If you got the "Database not found" error message, then please consider contacting the support team of your SOLIDWORKS Reseller (GoEngineer). Send them your model and your CWR files (very important). Then, ask them to contact SOLIDWORKS Simulation Tech Support so some manipulations can be done to try and solve the problem.
This happens to me all of the time. If you are unable to send your files to Solidworks for NDA purposes (that is my issue), there are a couple of things I have tried to fix this issue. Sometimes it works, sometimes it doesn't.
1. Copy your CWR files to another folder and point the Study to that folder.
2. Duplicate the Study. Make a copy of the CWR file and name it with the duplicated study name (note the naming convention on the CWR file is the "Assembly Name"-"Study Name".CWR)
3. With Solidworks closed, move all Simulation files out of your Simulation directory. Open your assembly and the study and try to load the results (you will be unsuccessful). Then close Solidworks and move the files back into the Simulation directory. Reopen the assembly and see if the link was restored (this is a long shot but it might work).
All in all, this is an ongoing issue that I struggle with constantly. I have contacted my Reseller who has talked with Solidworks Technical support and they told me to rerun the studies. Apparently the code that is saved in the assembly file to link to the CWR file is breaking for some reason. Maybe sending the model to them will produce different results. Good luck.