To clear the error:
You will not be able to open the Project but so long as it is the current project, you do not need to:
Click Analysis, Estimating, Job Resources.
Click each of the Resource Headers (Labour, Plant etc), when the correct Resource type is selected, the following error will be displayed, 'Result of calculation would be too large'.
Click OK. On the right, in the Price column, the word ERROR will be visible.
In the top right, click Allow Changes.
Select the Rate cell and overtype the current figure with a zero.
Close the Resource window.
Open the Estimating module and find the Item with the incorrect Quantity that has caused the error, usually the last item worked on.
Clear the incorrect Quantity and re-enter the Rate for the resource.
Click Tools, Check Job.
Run through the Job Checks (Preview, OK). You may received some error messages, OK through these and they should be cleared resulting in a Print Page Report.
If the problem project is not your current one, please continue with a support engineer so they can edit your configuration to make it current.
If your ConQuest is crashing just after the project opens then the configuration will need to be edited to stop the project loading so you can do the above. It is probably best to check with support before attempting this if you are not 100% confident you know where your configuration folder is.
If you are sure and you are not on any hosted environment, then edit the settings.ini within your configuration folder and find the [startup] section. Remove the rest of the line after tab= (probably Estimating), save the file and next time you open ConQuest, it should go to the Project Register, allowing you to carry out the steps above.