Sometimes, when validating a connection or updating the repository configuration for HP ALM, Tasktop can freeze due to a race condition in the transport library used by the HP ALM connector. This has most commonly been observed with HP ALM 11.5, but may affect other versions of HP ALM.
As a workaround, this can often be resolved by disabling network compression if it is enabled, or enabling it if it is disabled. To do this for your repository, open the Task Repositories view (Window -> Show View -> Other -> Mylyn -> Task Repositories), right click on your HP ALM repository and select Properties, and, under Advanced Settings, check or uncheck Enable network compression.
If you are still experiencing problems after changing this setting, please contact firstname.lastname@example.org.