I've never heard of .ism files.
As this is primarily a user to user forum, someone-else may chip in. But please remember that the same symptoms do not necessarily mean the same problem.
Meanwhile, the best thing to do is
contact Support, via here. There is a link at the top of the Search FAQs page to the Technical Support form, for some one to one investigation and help.
And, to help others who run into a similar problem, please let us know what you did to resolve the problem. Please do not quote directly any correspondence from Support, as that may apply only to your particular circumstances.