The other possibility is that Tracked Packet on PayPal has a bug. If you go and use another service first such as Small Packet, then switch to Tracked Packet, the PayPal page does not reset properly. What I do is chose "select Service" in the drop down list, then go to the bottom to continues and it says an error, then try Tracked Packet again and it usually works. This "trick" seems to reset the PayPal shipping page to work.
I still advise against mixing inches and grams if it does work. I never tried mixing and even if it appears to work, I would be wary of any result. Canada Post went metric in the 1970s and tables are in metric.
As for the comment above that metric is more accurate, it may sound silly because both metric and imperial systems are accurate and interchangeable in the real world. However, on eBay and PayPal, the data entry boxes only use whole numbers in the forms. So measuring to the nearest cm is finer than measuring to the nearest inch. (You are supposed to round up to the next highest cm or inch and not down.) (1 inch = 2.54 cm) Same with measuring to the nearest gram is finer than the measuring to the nearest ounce. (Again rounding up to the nearest ounce.) (1 ounce = 28 grams) So metric is more accurate (finer) than the imperial system on eBay/PayPal systems even though they should not be.
The round up in using imperial will cause you sometimes to go over a dimension or weight break point in the Canada Post rate tables. So to minimize round up issues and paying more than you should, use metric to be more accurate when using eBay/PayPal.
