Are there any size limitations for files that can be attached to reports?

There is no limit to the file size that can be attached, but you can limit a size of the Export file in "Restriction of Export File Size" field, which is displayed by selecting "Control Change" button on the "Menu" screen. FYI : Setting it to "0" will make it unlimited. If the file size is too large, please review attached file or separate Export period accordingly.