ETABS equation solutions are performed in double precision arithmetic, which allows for 15 significant figures. If you have global or local instability (e.g., a node that is not restrained), the solution will suffer a loss of accuracy. The program issues a warning if the loss is estimated to be above 6 digits, and will cease processing if the detected loss is above 11 digits. If you have an analysis where the number of digits lost is less than 8 for example, you should verify the results by checking where the errors are coming from, and also the *.OUT file to make sure the applied load and the reaction are in balance within 1% of each other. Loss messages can be a result of having very stiff elements together with very flexible elements. The rigid diaphragm assumption together with flexible elements is one example of this discrepancy.