SSRS Report Export Error

We have few Customized SSRS Reports, The problem is that when user try to Export the generated report in to PDF, EXCEL or any other format, following error appears:

An Error has occurred in the script on this page…
Could not complete the operation due to error 8150002e…

Did any one find out this kind of error ?

Note: This error occurrs seldomly with any of the user, so could not conclude specifically.

Any Update on this ?
this is happening with few of the users, and Epicor says this is not Epicor Issue,
Please suggest !