When two channel identifiers have the beginning of their identifier which is equal, and that beginning is equal or greater than 63 characters, this results in a "Duplicate definition" error at syntax checking.
For example, if you open a brand new UPPAAL modeling, put the following lines in the declaration section, you obtain a "duplicate definition" error.
urgent chan ttttttttttttttttttttttttttttttttttttttttttttttttttttttttttttttt1;
urgent chan ttttttttttttttttttttttttttttttttttttttttttttttttttttttttttttttt2;
I've seen no such restrictions mentioned in the grammar, but I may have missed that information.
By the way, I found this bug because I have written a UML-to-UPPAAL automatic code generator which may generate long channel names.
Fixed in revision 3780 in both 4.0 and trunk.
*** Bug 450 has been marked as a duplicate of this bug. ***