And what error do you get when you code a WIDTH= parameter? Also, you may want to share the entire PROC REPORT invocation code, as it appears in the SAS log window/output for more accurate review and response.
The WIDTH= option in PROC REPORT is ignored by ODS destinations, such as ODS HTML, ODS CSV and ODS TAGSETS.EXCELXP. Depending on what else you're doing, this error message sometimes results because the LISTING destination is still open and has determined that the width of your PROC REPORT report rows are greater than the current LISTING destination LINESIZE option.
...your solution is usually to close the LISTING destination. Of course, you might also want LISTING -and- HTML output, in which case, you could:
1) increase the LINESIZE on the options statement
2) increase the LINESIZE on the PROC REPORT statement
3) double check WIDTH= on your DEFINE statements
but remember that these 3 "tweaks" will work for LISTING only and are irrelevant to HTML files created with ODS.
Since, from your HTMLSTYLE override, I see that you are using the mso-number-format, it seems to me that you must be creating an HTML file to open with Excel. In this case, simply closing the LISTING destination should get rid of the error message.