Thank for contacting us on this.
May I please ask you to tell me if you are working on a sandbox, and if yes - please check if this sandbox was moved to the Summer'18 Salesforce version?
In this case, we are aware of a reason for the issue:
there are some updates in the log file structure on the updated environments - some entries have another structure and a changed set of parameters; this is why the IDE cannot parse your log file properly to start a debugging session.
Our developers are already working on this and we are going to release the necessary changes to solve the issue the nearest days.
If your log file wasn't generated on a sandbox with Summer'18 updates, I kindly ask you to send us a bug report directly from the IDE - you can find this functionality in the menu Help -> Report a Bug, please put your email and enable the 'Attach Log File' checkbox. This way we will receive your TWS log files which could provide us with an additional information about a reason for the error.