If you are receiving the error message "Error: You can't use more than X characters", it indicates you are over the character limit allowed when modifying a field. 

If you're seeing fewer characters than what is allowed for the field, it it typically due to content being copy and pasted from a third party source such as Microsoft Word or a website. These often contain hidden formatting, which is causing you to run into character count limits. 

Solution: To avoid this error, copy content from a plain text editor like Notepad. You will lose some formatting aspects but it will resolve the issue of going over the allotted character limit. 

If you are working in a Rich Text Area (RTA) field, some special characters are encoded upon input even when copied as plain text. A single apostrophe, as an example, encodes as 5 characters despite appearing as only one.